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 $69.43   5.767%   $73.434   $73.43   $73.45   $73.40  
  Purchase #2 $24.53   13.843%   $27.9257   $27.93   $27.95   $27.90  
  Purchase #3 $109.43   13.397%   $124.0903   $124.09   $124.10   $124.10  
  Purchase #4 $107.69   5.342%   $113.4428   $113.44   $113.45   $113.40  
  Purchase #5 $249.53   3.472%   $258.1937   $258.19   $258.20   $258.20  
  Purchase #6 $248.65   10.352%   $274.3902   $274.39   $274.40   $274.40  
  Purchase #7 $176.29   4.462%   $184.1561   $184.16   $184.15   $184.20  
  7 purchase totals = $985.55       $1,055.6328   $1,055.63   $1,055.70   $1,055.60