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 $108.86   6.783%   $116.244   $116.24   $116.25   $116.20  
  Purchase #2 $117.38   6.572%   $125.0942   $125.09   $125.10   $125.10  
  Purchase #3 $141.26   11.766%   $157.8807   $157.88   $157.90   $157.90  
  Purchase #4 $44.78   4.210%   $46.6652   $46.67   $46.65   $46.70  
  Purchase #5 $165.54   13.716%   $188.2455   $188.25   $188.25   $188.20  
  Purchase #6 $228.61   5.355%   $240.8521   $240.85   $240.85   $240.90  
  Purchase #7 $18.73   12.162%   $21.0079   $21.01   $21.00   $21.00  
  7 purchase totals = $825.16       $895.9896   $895.99   $896.00   $896.00