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 $75.99   12.202%   $85.2623   $85.26   $85.25   $85.30  
  Purchase #2 $123.82   8.218%   $133.9955   $134.00   $134.00   $134.00  
  Purchase #3 $106.38   11.566%   $118.6839   $118.68   $118.70   $118.70  
  Purchase #4 $8.82   4.648%   $9.23   $9.23   $9.25   $9.20  
  Purchase #5 $173.32   12.691%   $195.316   $195.32   $195.30   $195.30  
  Purchase #6 $36.63   11.825%   $40.9615   $40.96   $40.95   $41.00  
  Purchase #7 $221.46   8.614%   $240.5366   $240.54   $240.55   $240.50  
  7 purchase totals = $746.42       $823.9858   $823.99   $824.00   $824.00