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 $56.94   10.305%   $62.8077   $62.81   $62.80   $62.80  
  Purchase #2 $69.68   9.456%   $76.2689   $76.27   $76.25   $76.30  
  Purchase #3 $150.82   6.586%   $160.753   $160.75   $160.75   $160.80  
  Purchase #4 $9.66   4.577%   $10.1021   $10.10   $10.10   $10.10  
  Purchase #5 $107.63   6.282%   $114.3913   $114.39   $114.40   $114.40  
  Purchase #6 $134.89   12.512%   $151.7674   $151.77   $151.75   $151.80  
  Purchase #7 $231.85   10.493%   $256.178   $256.18   $256.20   $256.20  
  7 purchase totals = $761.47       $832.2684   $832.27   $832.25   $832.40