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 $116.46   13.275%   $131.9201   $131.92   $131.90   $131.90  
  Purchase #2 $92.44   12.293%   $103.8036   $103.80   $103.80   $103.80  
  Purchase #3 $13.47   12.525%   $15.1571   $15.16   $15.15   $15.20  
  Purchase #4 $72.63   4.242%   $75.711   $75.71   $75.70   $75.70  
  Purchase #5 $158.51   9.289%   $173.234   $173.23   $173.25   $173.20  
  Purchase #6 $94.69   4.817%   $99.2512   $99.25   $99.25   $99.30  
  Purchase #7 $249.62   6.427%   $265.6631   $265.66   $265.65   $265.70  
  7 purchase totals = $797.82       $864.7401   $864.73   $864.70   $864.80