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 $177.33   11.472%   $197.6733   $197.67   $197.65   $197.70  
  Purchase #2 $129.61   9.512%   $141.9385   $141.94   $141.95   $141.90  
  Purchase #3 $218.43   11.104%   $242.6845   $242.68   $242.70   $242.70  
  Purchase #4 $156.68   3.252%   $161.7752   $161.78   $161.80   $161.80  
  Purchase #5 $158.86   4.804%   $166.4916   $166.49   $166.50   $166.50  
  Purchase #6 $101.73   12.687%   $114.6365   $114.64   $114.65   $114.60  
  Purchase #7 $232.40   7.336%   $249.4489   $249.45   $249.45   $249.40  
  7 purchase totals = $1,175.04       $1,274.6485   $1,274.65   $1,274.70   $1,274.60