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 $248.55   6.605%   $264.9667   $264.97   $264.95   $265.00  
  Purchase #2 $221.61   8.584%   $240.633   $240.63   $240.65   $240.60  
  Purchase #3 $20.32   5.692%   $21.4766   $21.48   $21.50   $21.50  
  Purchase #4 $28.51   3.519%   $29.5133   $29.51   $29.50   $29.50  
  Purchase #5 $46.72   12.575%   $52.595   $52.60   $52.60   $52.60  
  Purchase #6 $195.56   7.766%   $210.7472   $210.75   $210.75   $210.70  
  Purchase #7 $79.89   11.644%   $89.1924   $89.19   $89.20   $89.20  
  7 purchase totals = $841.16       $909.1242   $909.13   $909.15   $909.10