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 $54.68   13.223%   $61.9103   $61.91   $61.90   $61.90  
  Purchase #2 $125.96   6.221%   $133.796   $133.80   $133.80   $133.80  
  Purchase #3 $198.34   9.574%   $217.3291   $217.33   $217.35   $217.30  
  Purchase #4 $72.35   5.584%   $76.39   $76.39   $76.40   $76.40  
  Purchase #5 $37.99   4.566%   $39.7246   $39.72   $39.70   $39.70  
  Purchase #6 $202.37   4.337%   $211.1468   $211.15   $211.15   $211.10  
  Purchase #7 $134.35   4.185%   $139.9725   $139.97   $139.95   $140.00  
  7 purchase totals = $826.04       $880.2693   $880.27   $880.25   $880.20