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 $82.47   11.562%   $92.0052   $92.01   $92.00   $92.00  
  Purchase #2 $102.64   13.622%   $116.6216   $116.62   $116.60   $116.60  
  Purchase #3 $99.75   10.824%   $110.5469   $110.55   $110.55   $110.50  
  Purchase #4 $208.85   4.730%   $218.7286   $218.73   $218.75   $218.70  
  Purchase #5 $217.45   8.616%   $236.1855   $236.19   $236.20   $236.20  
  Purchase #6 $47.30   3.259%   $48.8415   $48.84   $48.85   $48.80  
  Purchase #7 $160.97   5.473%   $169.7799   $169.78   $169.80   $169.80  
  7 purchase totals = $919.43       $992.7092   $992.72   $992.75   $992.60