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 $22.56   9.209%   $24.6376   $24.64   $24.65   $24.60  
  Purchase #2 $195.57   11.140%   $217.3565   $217.36   $217.35   $217.40  
  Purchase #3 $114.26   4.748%   $119.6851   $119.69   $119.70   $119.70  
  Purchase #4 $169.53   8.489%   $183.9214   $183.92   $183.90   $183.90  
  Purchase #5 $54.88   5.573%   $57.9385   $57.94   $57.95   $57.90  
  Purchase #6 $63.33   10.453%   $69.9499   $69.95   $69.95   $69.90  
  Purchase #7 $57.47   9.223%   $62.7705   $62.77   $62.75   $62.80  
  7 purchase totals = $677.60       $736.2595   $736.27   $736.25   $736.20