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 $82.97   13.216%   $93.9353   $93.94   $93.95   $93.90  
  Purchase #2 $174.61   4.390%   $182.2754   $182.28   $182.30   $182.30  
  Purchase #3 $234.54   3.376%   $242.4581   $242.46   $242.45   $242.50  
  Purchase #4 $134.41   10.830%   $148.9666   $148.97   $148.95   $149.00  
  Purchase #5 $90.91   13.456%   $103.1428   $103.14   $103.15   $103.10  
  Purchase #6 $46.63   7.463%   $50.11   $50.11   $50.10   $50.10  
  Purchase #7 $53.89   4.545%   $56.3393   $56.34   $56.35   $56.30  
  7 purchase totals = $817.96       $877.2275   $877.24   $877.25   $877.20