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 $28.98   11.251%   $32.2405   $32.24   $32.25   $32.20  
  Purchase #2 $125.88   10.455%   $139.0408   $139.04   $139.05   $139.00  
  Purchase #3 $222.26   5.412%   $234.2887   $234.29   $234.30   $234.30  
  Purchase #4 $82.93   8.427%   $89.9185   $89.92   $89.90   $89.90  
  Purchase #5 $191.54   12.272%   $215.0458   $215.05   $215.05   $215.00  
  Purchase #6 $247.90   8.562%   $269.1252   $269.13   $269.15   $269.10  
  Purchase #7 $56.70   12.267%   $63.6554   $63.66   $63.65   $63.70  
  7 purchase totals = $956.19       $1,043.3149   $1,043.33   $1,043.35   $1,043.20