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 $54.34   8.408%   $58.9089   $58.91   $58.90   $58.90  
  Purchase #2 $94.44   3.588%   $97.8285   $97.83   $97.85   $97.80  
  Purchase #3 $33.87   3.819%   $35.1635   $35.16   $35.15   $35.20  
  Purchase #4 $165.52   10.274%   $182.5255   $182.53   $182.55   $182.50  
  Purchase #5 $112.90   10.786%   $125.0774   $125.08   $125.10   $125.10  
  Purchase #6 $229.41   3.812%   $238.1551   $238.16   $238.15   $238.20  
  Purchase #7 $13.79   12.422%   $15.503   $15.50   $15.50   $15.50  
  7 purchase totals = $704.27       $753.1619   $753.17   $753.20   $753.20