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 $249.25   4.792%   $261.1941   $261.19   $261.20   $261.20  
  Purchase #2 $58.93   5.662%   $62.2666   $62.27   $62.25   $62.30  
  Purchase #3 $204.52   5.316%   $215.3923   $215.39   $215.40   $215.40  
  Purchase #4 $100.82   7.761%   $108.6446   $108.64   $108.65   $108.60  
  Purchase #5 $46.36   9.785%   $50.8963   $50.90   $50.90   $50.90  
  Purchase #6 $177.88   5.495%   $187.6545   $187.65   $187.65   $187.70  
  Purchase #7 $157.31   8.811%   $171.1706   $171.17   $171.15   $171.20  
  7 purchase totals = $995.07       $1,057.2190   $1,057.21   $1,057.20   $1,057.30