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 $230.71   13.114%   $260.9653   $260.97   $260.95   $261.00  
  Purchase #2 $41.81   11.844%   $46.762   $46.76   $46.75   $46.80  
  Purchase #3 $191.86   8.610%   $208.3791   $208.38   $208.40   $208.40  
  Purchase #4 $187.63   6.774%   $200.3401   $200.34   $200.35   $200.30  
  Purchase #5 $78.95   11.854%   $88.3087   $88.31   $88.30   $88.30  
  Purchase #6 $194.70   3.538%   $201.5885   $201.59   $201.60   $201.60  
  Purchase #7 $126.30   3.337%   $130.5146   $130.51   $130.50   $130.50  
  7 purchase totals = $1,051.96       $1,136.8583   $1,136.86   $1,136.85   $1,136.90