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 $61.42   4.559%   $64.2201   $64.22   $64.20   $64.20  
  Purchase #2 $66.64   9.509%   $72.9768   $72.98   $73.00   $73.00  
  Purchase #3 $202.90   3.817%   $210.6447   $210.64   $210.65   $210.60  
  Purchase #4 $93.34   4.503%   $97.5431   $97.54   $97.55   $97.50  
  Purchase #5 $235.41   12.628%   $265.1376   $265.14   $265.15   $265.10  
  Purchase #6 $236.69   5.796%   $250.4086   $250.41   $250.40   $250.40  
  Purchase #7 $13.36   5.788%   $14.1333   $14.13   $14.15   $14.10  
  7 purchase totals = $909.76       $975.0642   $975.06   $975.10   $974.90