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 $92.48   4.313%   $96.4687   $96.47   $96.45   $96.50  
  Purchase #2 $156.94   11.346%   $174.7464   $174.75   $174.75   $174.70  
  Purchase #3 $152.68   11.155%   $169.7115   $169.71   $169.70   $169.70  
  Purchase #4 $44.99   13.282%   $50.9656   $50.97   $50.95   $51.00  
  Purchase #5 $227.39   9.669%   $249.3763   $249.38   $249.40   $249.40  
  Purchase #6 $195.28   11.558%   $217.8505   $217.85   $217.85   $217.90  
  Purchase #7 $95.28   10.855%   $105.6226   $105.62   $105.60   $105.60  
  7 purchase totals = $965.04       $1,064.7416   $1,064.75   $1,064.70   $1,064.80