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 $139.63   11.437%   $155.5995   $155.60   $155.60   $155.60  
  Purchase #2 $248.75   7.622%   $267.7097   $267.71   $267.70   $267.70  
  Purchase #3 $104.32   10.300%   $115.065   $115.07   $115.05   $115.10  
  Purchase #4 $227.44   12.717%   $256.3635   $256.36   $256.35   $256.40  
  Purchase #5 $182.85   9.563%   $200.3359   $200.34   $200.35   $200.30  
  Purchase #6 $227.54   12.280%   $255.4819   $255.48   $255.50   $255.50  
  Purchase #7 $192.80   11.709%   $215.375   $215.38   $215.40   $215.40  
  7 purchase totals = $1,323.33       $1,465.9305   $1,465.94   $1,465.95   $1,466.00