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 $68.25   11.848%   $76.3363   $76.34   $76.35   $76.30  
  Purchase #2 $93.34   7.418%   $100.264   $100.26   $100.25   $100.30  
  Purchase #3 $36.75   11.262%   $40.8888   $40.89   $40.90   $40.90  
  Purchase #4 $179.43   10.132%   $197.6098   $197.61   $197.60   $197.60  
  Purchase #5 $106.37   13.498%   $120.7278   $120.73   $120.75   $120.70  
  Purchase #6 $53.68   11.296%   $59.7437   $59.74   $59.75   $59.70  
  Purchase #7 $86.71   8.870%   $94.4012   $94.40   $94.40   $94.40  
  7 purchase totals = $624.53       $689.9716   $689.97   $690.00   $689.90