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 $36.41   13.415%   $41.2944   $41.29   $41.30   $41.30  
  Purchase #2 $125.63   5.804%   $132.9216   $132.92   $132.90   $132.90  
  Purchase #3 $248.46   7.687%   $267.5591   $267.56   $267.55   $267.60  
  Purchase #4 $72.76   13.788%   $82.7921   $82.79   $82.80   $82.80  
  Purchase #5 $146.83   11.679%   $163.9783   $163.98   $164.00   $164.00  
  Purchase #6 $39.52   4.469%   $41.2861   $41.29   $41.30   $41.30  
  Purchase #7 $220.39   5.671%   $232.8883   $232.89   $232.90   $232.90  
  7 purchase totals = $890.00       $962.7199   $962.72   $962.75   $962.80