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 $247.57   8.382%   $268.3213   $268.32   $268.30   $268.30  
  Purchase #2 $93.38   7.632%   $100.5068   $100.51   $100.50   $100.50  
  Purchase #3 $193.82   6.610%   $206.6315   $206.63   $206.65   $206.60  
  Purchase #4 $56.82   9.681%   $62.3207   $62.32   $62.30   $62.30  
  Purchase #5 $234.39   10.521%   $259.0502   $259.05   $259.05   $259.10  
  Purchase #6 $193.56   8.745%   $210.4868   $210.49   $210.50   $210.50  
  Purchase #7 $140.63   10.738%   $155.7308   $155.73   $155.75   $155.70  
  7 purchase totals = $1,160.17       $1,263.0481   $1,263.05   $1,263.05   $1,263.00