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 $82.55   4.189%   $86.008   $86.01   $86.00   $86.00  
  Purchase #2 $18.99   11.328%   $21.1412   $21.14   $21.15   $21.10  
  Purchase #3 $72.73   4.515%   $76.0138   $76.01   $76.00   $76.00  
  Purchase #4 $239.68   10.781%   $265.5199   $265.52   $265.50   $265.50  
  Purchase #5 $205.89   10.651%   $227.8193   $227.82   $227.80   $227.80  
  Purchase #6 $70.48   6.778%   $75.2571   $75.26   $75.25   $75.30  
  Purchase #7 $37.83   13.809%   $43.0539   $43.05   $43.05   $43.10  
  7 purchase totals = $728.15       $794.8132   $794.81   $794.75   $794.80