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 $91.38   6.651%   $97.4577   $97.46   $97.45   $97.50  
  Purchase #2 $148.85   13.872%   $169.4985   $169.50   $169.50   $169.50  
  Purchase #3 $12.53   9.349%   $13.7014   $13.70   $13.70   $13.70  
  Purchase #4 $77.29   6.117%   $82.0178   $82.02   $82.00   $82.00  
  Purchase #5 $194.52   9.638%   $213.2678   $213.27   $213.25   $213.30  
  Purchase #6 $126.61   6.782%   $135.1967   $135.20   $135.20   $135.20  
  Purchase #7 $219.63   10.195%   $242.0213   $242.02   $242.00   $242.00  
  7 purchase totals = $870.81       $953.1612   $953.17   $953.10   $953.20