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 $67.71   13.380%   $76.7696   $76.77   $76.75   $76.80  
  Purchase #2 $149.85   10.717%   $165.9094   $165.91   $165.90   $165.90  
  Purchase #3 $191.72   6.615%   $204.4023   $204.40   $204.40   $204.40  
  Purchase #4 $125.61   13.571%   $142.6565   $142.66   $142.65   $142.70  
  Purchase #5 $234.52   11.475%   $261.4312   $261.43   $261.45   $261.40  
  Purchase #6 $55.68   5.746%   $58.8794   $58.88   $58.90   $58.90  
  Purchase #7 $42.86   5.650%   $45.2816   $45.28   $45.30   $45.30  
  7 purchase totals = $867.95       $955.3300   $955.33   $955.35   $955.40