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 $53.29   13.105%   $60.2737   $60.27   $60.25   $60.30  
  Purchase #2 $198.31   8.538%   $215.2417   $215.24   $215.25   $215.20  
  Purchase #3 $224.49   9.308%   $245.3855   $245.39   $245.40   $245.40  
  Purchase #4 $54.89   6.164%   $58.2734   $58.27   $58.25   $58.30  
  Purchase #5 $50.56   11.339%   $56.293   $56.29   $56.30   $56.30  
  Purchase #6 $159.56   12.163%   $178.9673   $178.97   $178.95   $179.00  
  Purchase #7 $61.35   11.781%   $68.5776   $68.58   $68.60   $68.60  
  7 purchase totals = $802.45       $883.0122   $883.01   $883.00   $883.10