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 $107.52   6.722%   $114.7475   $114.75   $114.75   $114.70  
  Purchase #2 $241.36   3.561%   $249.9548   $249.95   $249.95   $250.00  
  Purchase #3 $84.67   4.277%   $88.2913   $88.29   $88.30   $88.30  
  Purchase #4 $73.29   4.761%   $76.7793   $76.78   $76.80   $76.80  
  Purchase #5 $172.45   3.727%   $178.8772   $178.88   $178.90   $178.90  
  Purchase #6 $162.43   10.116%   $178.8614   $178.86   $178.85   $178.90  
  Purchase #7 $35.94   6.354%   $38.2236   $38.22   $38.20   $38.20  
  7 purchase totals = $877.66       $925.7351   $925.73   $925.75   $925.80