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 $55.47   5.532%   $58.5386   $58.54   $58.55   $58.50  
  Purchase #2 $193.47   9.436%   $211.7258   $211.73   $211.75   $211.70  
  Purchase #3 $230.45   11.630%   $257.2513   $257.25   $257.25   $257.30  
  Purchase #4 $198.50   9.353%   $217.0657   $217.07   $217.05   $217.10  
  Purchase #5 $81.31   12.477%   $91.455   $91.46   $91.45   $91.50  
  Purchase #6 $115.67   8.314%   $125.2868   $125.29   $125.30   $125.30  
  Purchase #7 $244.49   9.742%   $268.3082   $268.31   $268.30   $268.30  
  7 purchase totals = $1,119.36       $1,229.6314   $1,229.65   $1,229.65   $1,229.70