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 $58.70   13.202%   $66.4496   $66.45   $66.45   $66.40  
  Purchase #2 $114.82   4.267%   $119.7194   $119.72   $119.70   $119.70  
  Purchase #3 $94.93   4.313%   $99.0243   $99.02   $99.00   $99.00  
  Purchase #4 $245.63   6.422%   $261.4044   $261.40   $261.40   $261.40  
  Purchase #5 $48.95   8.692%   $53.2047   $53.20   $53.20   $53.20  
  Purchase #6 $227.62   10.674%   $251.9162   $251.92   $251.90   $251.90  
  Purchase #7 $138.35   9.673%   $151.7326   $151.73   $151.75   $151.70  
  7 purchase totals = $929.00       $1,003.4512   $1,003.44   $1,003.40   $1,003.30