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 $52.27   13.598%   $59.3777   $59.38   $59.40   $59.40  
  Purchase #2 $241.42   8.613%   $262.2135   $262.21   $262.20   $262.20  
  Purchase #3 $154.79   4.672%   $162.0218   $162.02   $162.00   $162.00  
  Purchase #4 $101.87   5.160%   $107.1265   $107.13   $107.15   $107.10  
  Purchase #5 $29.33   8.810%   $31.914   $31.91   $31.90   $31.90  
  Purchase #6 $64.53   4.157%   $67.2125   $67.21   $67.20   $67.20  
  Purchase #7 $245.32   6.312%   $260.8046   $260.80   $260.80   $260.80  
  7 purchase totals = $889.53       $950.6706   $950.66   $950.65   $950.60