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 $108.42   9.428%   $118.6418   $118.64   $118.65   $118.60  
  Purchase #2 $160.53   11.411%   $178.8481   $178.85   $178.85   $178.80  
  Purchase #3 $72.51   4.121%   $75.4981   $75.50   $75.50   $75.50  
  Purchase #4 $203.67   10.452%   $224.9576   $224.96   $224.95   $225.00  
  Purchase #5 $245.28   6.804%   $261.9689   $261.97   $261.95   $262.00  
  Purchase #6 $69.62   8.753%   $75.7138   $75.71   $75.70   $75.70  
  Purchase #7 $186.69   12.696%   $210.3922   $210.39   $210.40   $210.40  
  7 purchase totals = $1,046.72       $1,146.0205   $1,146.02   $1,146.00   $1,146.00