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 $224.67   13.205%   $254.3377   $254.34   $254.35   $254.30  
  Purchase #2 $119.54   11.451%   $133.2285   $133.23   $133.25   $133.20  
  Purchase #3 $44.80   5.242%   $47.1484   $47.15   $47.15   $47.10  
  Purchase #4 $245.62   7.733%   $264.6138   $264.61   $264.60   $264.60  
  Purchase #5 $149.75   13.356%   $169.7506   $169.75   $169.75   $169.80  
  Purchase #6 $63.96   13.705%   $72.7257   $72.73   $72.75   $72.70  
  Purchase #7 $215.78   13.118%   $244.086   $244.09   $244.10   $244.10  
  7 purchase totals = $1,064.12       $1,185.8907   $1,185.90   $1,185.95   $1,185.80