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 $62.36   6.709%   $66.5437   $66.54   $66.55   $66.50  
  Purchase #2 $236.97   8.188%   $256.3731   $256.37   $256.35   $256.40  
  Purchase #3 $31.80   4.133%   $33.1143   $33.11   $33.10   $33.10  
  Purchase #4 $79.63   4.297%   $83.0517   $83.05   $83.05   $83.10  
  Purchase #5 $31.77   8.735%   $34.5451   $34.55   $34.55   $34.50  
  Purchase #6 $214.65   10.558%   $237.3127   $237.31   $237.30   $237.30  
  Purchase #7 $111.41   5.688%   $117.747   $117.75   $117.75   $117.70  
  7 purchase totals = $768.59       $828.6876   $828.68   $828.65   $828.60