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 $172.80   12.828%   $194.9668   $194.97   $194.95   $195.00  
  Purchase #2 $236.51   9.393%   $258.7254   $258.73   $258.75   $258.70  
  Purchase #3 $12.79   7.177%   $13.7079   $13.71   $13.70   $13.70  
  Purchase #4 $114.37   11.319%   $127.3155   $127.32   $127.30   $127.30  
  Purchase #5 $230.98   12.314%   $259.4229   $259.42   $259.40   $259.40  
  Purchase #6 $43.93   6.321%   $46.7068   $46.71   $46.70   $46.70  
  Purchase #7 $51.32   10.571%   $56.745   $56.75   $56.75   $56.70  
  7 purchase totals = $862.70       $957.5903   $957.61   $957.55   $957.50