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 $238.97   9.443%   $261.5359   $261.54   $261.55   $261.50  
  Purchase #2 $186.88   9.808%   $205.2092   $205.21   $205.20   $205.20  
  Purchase #3 $36.82   11.660%   $41.1132   $41.11   $41.10   $41.10  
  Purchase #4 $37.67   8.552%   $40.8915   $40.89   $40.90   $40.90  
  Purchase #5 $128.29   5.555%   $135.4165   $135.42   $135.40   $135.40  
  Purchase #6 $44.92   9.105%   $49.01   $49.01   $49.00   $49.00  
  Purchase #7 $58.49   10.373%   $64.5572   $64.56   $64.55   $64.60  
  7 purchase totals = $732.04       $797.7335   $797.74   $797.70   $797.70