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 $176.87   10.364%   $195.2008   $195.20   $195.20   $195.20  
  Purchase #2 $11.65   8.286%   $12.6153   $12.62   $12.60   $12.60  
  Purchase #3 $44.50   12.806%   $50.1987   $50.20   $50.20   $50.20  
  Purchase #4 $165.63   4.632%   $173.302   $173.30   $173.30   $173.30  
  Purchase #5 $166.39   11.126%   $184.9026   $184.90   $184.90   $184.90  
  Purchase #6 $164.42   5.756%   $173.884   $173.88   $173.90   $173.90  
  Purchase #7 $36.30   7.865%   $39.155   $39.16   $39.15   $39.20  
  7 purchase totals = $765.76       $829.2584   $829.26   $829.25   $829.30