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 $244.38   11.523%   $272.5399   $272.54   $272.55   $272.50  
  Purchase #2 $176.91   3.177%   $182.5304   $182.53   $182.55   $182.50  
  Purchase #3 $221.27   4.108%   $230.3598   $230.36   $230.35   $230.40  
  Purchase #4 $92.62   9.563%   $101.4773   $101.48   $101.50   $101.50  
  Purchase #5 $248.95   10.166%   $274.2583   $274.26   $274.25   $274.30  
  Purchase #6 $193.26   7.479%   $207.7139   $207.71   $207.70   $207.70  
  Purchase #7 $95.57   3.542%   $98.9551   $98.96   $98.95   $99.00  
  7 purchase totals = $1,272.96       $1,367.8347   $1,367.84   $1,367.85   $1,367.90