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 $6.88   8.466%   $7.4625   $7.46   $7.45   $7.50  
  Purchase #2 $203.33   3.549%   $210.5462   $210.55   $210.55   $210.50  
  Purchase #3 $96.36   6.551%   $102.6725   $102.67   $102.65   $102.70  
  Purchase #4 $24.97   6.735%   $26.6517   $26.65   $26.65   $26.70  
  Purchase #5 $82.88   13.356%   $93.9495   $93.95   $93.95   $93.90  
  Purchase #6 $146.97   4.177%   $153.1089   $153.11   $153.10   $153.10  
  Purchase #7 $105.80   12.525%   $119.0515   $119.05   $119.05   $119.10  
  7 purchase totals = $667.19       $713.4428   $713.44   $713.40   $713.50