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 $240.41   11.464%   $267.9706   $267.97   $267.95   $268.00  
  Purchase #2 $184.86   10.792%   $204.8101   $204.81   $204.80   $204.80  
  Purchase #3 $198.42   9.806%   $217.8771   $217.88   $217.90   $217.90  
  Purchase #4 $146.60   7.817%   $158.0597   $158.06   $158.05   $158.10  
  Purchase #5 $87.95   8.190%   $95.1531   $95.15   $95.15   $95.20  
  Purchase #6 $122.46   7.218%   $131.2992   $131.30   $131.30   $131.30  
  Purchase #7 $63.94   3.483%   $66.167   $66.17   $66.15   $66.20  
  7 purchase totals = $1,044.64       $1,141.3368   $1,141.34   $1,141.30   $1,141.50