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 $235.48   8.610%   $255.7548   $255.75   $255.75   $255.80  
  Purchase #2 $200.51   8.520%   $217.5935   $217.59   $217.60   $217.60  
  Purchase #3 $219.46   9.542%   $240.4009   $240.40   $240.40   $240.40  
  Purchase #4 $194.71   6.208%   $206.7976   $206.80   $206.80   $206.80  
  Purchase #5 $21.88   3.311%   $22.6044   $22.60   $22.60   $22.60  
  Purchase #6 $204.28   5.738%   $216.0016   $216.00   $216.00   $216.00  
  Purchase #7 $121.63   4.103%   $126.6205   $126.62   $126.60   $126.60  
  7 purchase totals = $1,197.95       $1,285.7733   $1,285.76   $1,285.75   $1,285.80