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 $125.39   7.824%   $135.2005   $135.20   $135.20   $135.20  
  Purchase #2 $234.38   12.428%   $263.5087   $263.51   $263.50   $263.50  
  Purchase #3 $48.73   10.760%   $53.9733   $53.97   $53.95   $54.00  
  Purchase #4 $111.69   4.388%   $116.591   $116.59   $116.60   $116.60  
  Purchase #5 $238.73   9.557%   $261.5454   $261.55   $261.55   $261.50  
  Purchase #6 $86.77   13.647%   $98.6115   $98.61   $98.60   $98.60  
  Purchase #7 $91.63   9.564%   $100.3935   $100.39   $100.40   $100.40  
  7 purchase totals = $937.32       $1,029.8239   $1,029.82   $1,029.80   $1,029.80