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 $176.91   10.605%   $195.6713   $195.67   $195.65   $195.70  
  Purchase #2 $185.86   7.177%   $199.1992   $199.20   $199.20   $199.20  
  Purchase #3 $17.82   8.107%   $19.2647   $19.26   $19.25   $19.30  
  Purchase #4 $146.71   9.240%   $160.266   $160.27   $160.25   $160.30  
  Purchase #5 $91.78   10.851%   $101.739   $101.74   $101.75   $101.70  
  Purchase #6 $165.74   13.205%   $187.626   $187.63   $187.65   $187.60  
  Purchase #7 $40.97   7.614%   $44.0895   $44.09   $44.10   $44.10  
  7 purchase totals = $825.79       $907.8557   $907.86   $907.85   $907.90