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 $249.27   7.116%   $267.0081   $267.01   $267.00   $267.00  
  Purchase #2 $72.50   4.636%   $75.8611   $75.86   $75.85   $75.90  
  Purchase #3 $65.53   3.208%   $67.6322   $67.63   $67.65   $67.60  
  Purchase #4 $184.89   5.588%   $195.2217   $195.22   $195.20   $195.20  
  Purchase #5 $162.53   4.102%   $169.197   $169.20   $169.20   $169.20  
  Purchase #6 $73.62   6.524%   $78.423   $78.42   $78.40   $78.40  
  Purchase #7 $154.82   7.378%   $166.2426   $166.24   $166.25   $166.20  
  7 purchase totals = $963.16       $1,019.5857   $1,019.58   $1,019.55   $1,019.50