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 $57.25   12.396%   $64.3467   $64.35   $64.35   $64.30  
  Purchase #2 $32.38   13.178%   $36.647   $36.65   $36.65   $36.60  
  Purchase #3 $214.32   3.755%   $222.3677   $222.37   $222.35   $222.40  
  Purchase #4 $15.69   8.669%   $17.0502   $17.05   $17.05   $17.10  
  Purchase #5 $35.96   4.526%   $37.5875   $37.59   $37.60   $37.60  
  Purchase #6 $246.28   5.765%   $260.478   $260.48   $260.50   $260.50  
  Purchase #7 $155.26   4.793%   $162.7016   $162.70   $162.70   $162.70  
  7 purchase totals = $757.14       $801.1787   $801.19   $801.20   $801.20