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 $94.63   13.222%   $107.142   $107.14   $107.15   $107.10  
  Purchase #2 $86.97   13.789%   $98.9623   $98.96   $98.95   $99.00  
  Purchase #3 $79.79   13.148%   $90.2808   $90.28   $90.30   $90.30  
  Purchase #4 $151.50   7.569%   $162.967   $162.97   $162.95   $163.00  
  Purchase #5 $176.73   5.268%   $186.0401   $186.04   $186.05   $186.00  
  Purchase #6 $7.64   8.554%   $8.2935   $8.29   $8.30   $8.30  
  Purchase #7 $238.91   12.128%   $267.885   $267.89   $267.90   $267.90  
  7 purchase totals = $836.17       $921.5707   $921.57   $921.60   $921.60