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 $101.81   4.713%   $106.6083   $106.61   $106.60   $106.60  
  Purchase #2 $73.86   11.362%   $82.252   $82.25   $82.25   $82.30  
  Purchase #3 $183.64   6.166%   $194.9632   $194.96   $194.95   $195.00  
  Purchase #4 $153.59   10.550%   $169.7937   $169.79   $169.80   $169.80  
  Purchase #5 $164.63   11.492%   $183.5493   $183.55   $183.55   $183.50  
  Purchase #6 $64.84   6.575%   $69.1032   $69.10   $69.10   $69.10  
  Purchase #7 $66.93   13.388%   $75.8906   $75.89   $75.90   $75.90  
  7 purchase totals = $809.30       $882.1603   $882.15   $882.15   $882.20