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 $59.27   6.105%   $62.8884   $62.89   $62.90   $62.90  
  Purchase #2 $171.53   13.412%   $194.5356   $194.54   $194.55   $194.50  
  Purchase #3 $72.52   9.707%   $79.5595   $79.56   $79.55   $79.60  
  Purchase #4 $229.40   10.158%   $252.7025   $252.70   $252.70   $252.70  
  Purchase #5 $125.48   5.207%   $132.0137   $132.01   $132.00   $132.00  
  Purchase #6 $78.95   8.569%   $85.7152   $85.72   $85.70   $85.70  
  Purchase #7 $26.74   7.753%   $28.8132   $28.81   $28.80   $28.80  
  7 purchase totals = $763.89       $836.2281   $836.23   $836.20   $836.20