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 $76.38   9.499%   $83.6353   $83.64   $83.65   $83.60  
  Purchase #2 $238.81   5.487%   $251.9135   $251.91   $251.90   $251.90  
  Purchase #3 $198.60   4.704%   $207.9421   $207.94   $207.95   $207.90  
  Purchase #4 $197.40   13.700%   $224.4438   $224.44   $224.45   $224.40  
  Purchase #5 $54.26   11.117%   $60.2921   $60.29   $60.30   $60.30  
  Purchase #6 $146.46   13.782%   $166.6451   $166.65   $166.65   $166.60  
  Purchase #7 $224.87   10.710%   $248.9536   $248.95   $248.95   $249.00  
  7 purchase totals = $1,136.78       $1,243.8255   $1,243.82   $1,243.85   $1,243.70