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 $61.25   11.423%   $68.2466   $68.25   $68.25   $68.20  
  Purchase #2 $141.74   8.261%   $153.4491   $153.45   $153.45   $153.40  
  Purchase #3 $74.87   7.739%   $80.6642   $80.66   $80.65   $80.70  
  Purchase #4 $87.92   4.279%   $91.6821   $91.68   $91.70   $91.70  
  Purchase #5 $61.63   8.181%   $66.672   $66.67   $66.65   $66.70  
  Purchase #6 $33.78   4.429%   $35.2761   $35.28   $35.30   $35.30  
  Purchase #7 $198.55   9.735%   $217.8788   $217.88   $217.90   $217.90  
  7 purchase totals = $659.74       $713.8689   $713.87   $713.90   $713.90