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 $237.46   6.525%   $252.9543   $252.95   $252.95   $253.00  
  Purchase #2 $73.82   9.411%   $80.7672   $80.77   $80.75   $80.80  
  Purchase #3 $54.96   11.658%   $61.3672   $61.37   $61.35   $61.40  
  Purchase #4 $195.38   10.302%   $215.508   $215.51   $215.50   $215.50  
  Purchase #5 $19.35   4.354%   $20.1925   $20.19   $20.20   $20.20  
  Purchase #6 $123.40   13.428%   $139.9702   $139.97   $139.95   $140.00  
  Purchase #7 $182.80   3.717%   $189.5947   $189.59   $189.60   $189.60  
  7 purchase totals = $887.17       $960.3541   $960.35   $960.30   $960.50