Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $104.79   10.182%   $115.4597   $115.46   $115.45   $115.50  
  Purchase #2 $229.98   6.803%   $245.6255   $245.63   $245.65   $245.60  
  Purchase #3 $250.67   13.570%   $284.6859   $284.69   $284.70   $284.70  
  Purchase #4 $244.31   9.764%   $268.1644   $268.16   $268.15   $268.20  
  Purchase #5 $130.27   12.246%   $146.2229   $146.22   $146.20   $146.20  
  Purchase #6 $124.73   5.247%   $131.2746   $131.27   $131.25   $131.30  
  Purchase #7 $235.47   4.526%   $246.1274   $246.13   $246.15   $246.10  
  7 purchase totals = $1,320.22       $1,437.5604   $1,437.56   $1,437.55   $1,437.60