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 $63.26   4.559%   $66.144   $66.14   $66.15   $66.10  
  Purchase #2 $81.87   3.249%   $84.53   $84.53   $84.55   $84.50  
  Purchase #3 $148.97   5.499%   $157.1619   $157.16   $157.15   $157.20  
  Purchase #4 $247.89   10.706%   $274.4291   $274.43   $274.45   $274.40  
  Purchase #5 $219.30   10.779%   $242.9383   $242.94   $242.95   $242.90  
  Purchase #6 $221.50   8.271%   $239.8203   $239.82   $239.80   $239.80  
  Purchase #7 $196.54   3.472%   $203.3639   $203.36   $203.35   $203.40  
  7 purchase totals = $1,179.33       $1,268.3875   $1,268.38   $1,268.40   $1,268.30