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 $149.32   3.233%   $154.1475   $154.15   $154.15   $154.10  
  Purchase #2 $239.50   11.580%   $267.2341   $267.23   $267.25   $267.20  
  Purchase #3 $178.38   9.157%   $194.7143   $194.71   $194.70   $194.70  
  Purchase #4 $178.44   6.259%   $189.6086   $189.61   $189.60   $189.60  
  Purchase #5 $44.57   13.177%   $50.443   $50.44   $50.45   $50.40  
  Purchase #6 $126.68   5.712%   $133.916   $133.92   $133.90   $133.90  
  Purchase #7 $247.59   7.798%   $266.8971   $266.90   $266.90   $266.90  
  7 purchase totals = $1,164.48       $1,256.9606   $1,256.96   $1,256.95   $1,256.80