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 $68.27   7.186%   $73.1759   $73.18   $73.20   $73.20  
  Purchase #2 $173.86   11.314%   $193.5305   $193.53   $193.55   $193.50  
  Purchase #3 $40.71   3.300%   $42.0534   $42.05   $42.05   $42.10  
  Purchase #4 $173.38   6.499%   $184.648   $184.65   $184.65   $184.60  
  Purchase #5 $154.52   4.384%   $161.2942   $161.29   $161.30   $161.30  
  Purchase #6 $58.31   7.783%   $62.8483   $62.85   $62.85   $62.80  
  Purchase #7 $125.71   11.640%   $140.3426   $140.34   $140.35   $140.30  
  7 purchase totals = $794.76       $857.8929   $857.89   $857.95   $857.80