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 $217.84   10.294%   $240.2644   $240.26   $240.25   $240.30  
  Purchase #2 $136.99   3.272%   $141.4723   $141.47   $141.45   $141.50  
  Purchase #3 $238.37   3.534%   $246.794   $246.79   $246.80   $246.80  
  Purchase #4 $250.30   6.809%   $267.3429   $267.34   $267.35   $267.30  
  Purchase #5 $225.73   4.507%   $235.9037   $235.90   $235.90   $235.90  
  Purchase #6 $16.99   3.517%   $17.5875   $17.59   $17.60   $17.60  
  Purchase #7 $80.56   3.447%   $83.3369   $83.34   $83.35   $83.30  
  7 purchase totals = $1,166.78       $1,232.7017   $1,232.69   $1,232.70   $1,232.70