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 $247.33   3.586%   $256.1993   $256.20   $256.20   $256.20  
  Purchase #2 $69.62   8.749%   $75.7111   $75.71   $75.70   $75.70  
  Purchase #3 $167.36   8.839%   $182.153   $182.15   $182.15   $182.20  
  Purchase #4 $173.78   6.405%   $184.9106   $184.91   $184.90   $184.90  
  Purchase #5 $127.88   5.338%   $134.7062   $134.71   $134.70   $134.70  
  Purchase #6 $59.37   13.492%   $67.3802   $67.38   $67.40   $67.40  
  Purchase #7 $35.83   11.767%   $40.0461   $40.05   $40.05   $40.00  
  7 purchase totals = $881.17       $941.1065   $941.11   $941.10   $941.10