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 $233.37   4.694%   $244.3244   $244.32   $244.30   $244.30  
  Purchase #2 $35.59   11.546%   $39.6992   $39.70   $39.70   $39.70  
  Purchase #3 $119.42   12.154%   $133.9343   $133.93   $133.95   $133.90  
  Purchase #4 $109.40   4.321%   $114.1272   $114.13   $114.15   $114.10  
  Purchase #5 $215.69   9.694%   $236.599   $236.60   $236.60   $236.60  
  Purchase #6 $69.45   10.687%   $76.8721   $76.87   $76.85   $76.90  
  Purchase #7 $14.53   10.808%   $16.1004   $16.10   $16.10   $16.10  
  7 purchase totals = $797.45       $861.6566   $861.65   $861.65   $861.60