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 $30.78   10.338%   $33.962   $33.96   $33.95   $34.00  
  Purchase #2 $86.35   8.275%   $93.4955   $93.50   $93.50   $93.50  
  Purchase #3 $240.62   9.147%   $262.6295   $262.63   $262.65   $262.60  
  Purchase #4 $184.26   8.195%   $199.3601   $199.36   $199.35   $199.40  
  Purchase #5 $98.69   11.533%   $110.0719   $110.07   $110.05   $110.10  
  Purchase #6 $70.77   7.605%   $76.1521   $76.15   $76.15   $76.20  
  Purchase #7 $151.27   9.652%   $165.8706   $165.87   $165.85   $165.90  
  7 purchase totals = $862.74       $941.5417   $941.54   $941.50   $941.70