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 $66.86   8.831%   $72.7644   $72.76   $72.75   $72.80  
  Purchase #2 $57.67   9.653%   $63.2369   $63.24   $63.25   $63.20  
  Purchase #3 $209.44   9.686%   $229.7264   $229.73   $229.75   $229.70  
  Purchase #4 $80.36   10.277%   $88.6186   $88.62   $88.60   $88.60  
  Purchase #5 $154.95   3.303%   $160.068   $160.07   $160.05   $160.10  
  Purchase #6 $148.49   8.809%   $161.5705   $161.57   $161.55   $161.60  
  Purchase #7 $209.38   8.612%   $227.4118   $227.41   $227.40   $227.40  
  7 purchase totals = $927.15       $1,003.3966   $1,003.40   $1,003.35   $1,003.40