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 $248.87   7.524%   $267.595   $267.60   $267.60   $267.60  
  Purchase #2 $90.95   12.542%   $102.3569   $102.36   $102.35   $102.40  
  Purchase #3 $79.72   12.172%   $89.4235   $89.42   $89.40   $89.40  
  Purchase #4 $201.99   12.524%   $227.2872   $227.29   $227.30   $227.30  
  Purchase #5 $56.64   11.267%   $63.0216   $63.02   $63.00   $63.00  
  Purchase #6 $14.80   10.770%   $16.394   $16.39   $16.40   $16.40  
  Purchase #7 $129.46   6.811%   $138.2775   $138.28   $138.30   $138.30  
  7 purchase totals = $822.43       $904.3557   $904.36   $904.35   $904.40