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 $208.84   13.303%   $236.622   $236.62   $236.60   $236.60  
  Purchase #2 $174.25   3.733%   $180.7548   $180.75   $180.75   $180.80  
  Purchase #3 $233.63   9.862%   $256.6706   $256.67   $256.65   $256.70  
  Purchase #4 $248.48   6.376%   $264.3231   $264.32   $264.30   $264.30  
  Purchase #5 $86.51   9.503%   $94.731   $94.73   $94.75   $94.70  
  Purchase #6 $170.80   6.552%   $181.9908   $181.99   $182.00   $182.00  
  Purchase #7 $176.84   5.801%   $187.0985   $187.10   $187.10   $187.10  
  7 purchase totals = $1,299.35       $1,402.1908   $1,402.18   $1,402.15   $1,402.20