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 $60.96   10.713%   $67.4906   $67.49   $67.50   $67.50  
  Purchase #2 $221.60   12.740%   $249.8318   $249.83   $249.85   $249.80  
  Purchase #3 $225.39   8.339%   $244.1853   $244.19   $244.20   $244.20  
  Purchase #4 $93.39   10.766%   $103.4444   $103.44   $103.45   $103.40  
  Purchase #5 $190.87   3.863%   $198.2433   $198.24   $198.25   $198.20  
  Purchase #6 $225.91   8.642%   $245.4331   $245.43   $245.45   $245.40  
  Purchase #7 $178.93   6.531%   $190.6159   $190.62   $190.60   $190.60  
  7 purchase totals = $1,197.05       $1,299.2444   $1,299.24   $1,299.30   $1,299.10