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 $49.83   9.346%   $54.4871   $54.49   $54.50   $54.50  
  Purchase #2 $130.96   4.821%   $137.2736   $137.27   $137.25   $137.30  
  Purchase #3 $241.80   8.336%   $261.9564   $261.96   $261.95   $262.00  
  Purchase #4 $40.91   4.461%   $42.735   $42.74   $42.75   $42.70  
  Purchase #5 $108.34   7.607%   $116.5814   $116.58   $116.60   $116.60  
  Purchase #6 $236.65   9.702%   $259.6098   $259.61   $259.60   $259.60  
  Purchase #7 $126.95   8.343%   $137.5414   $137.54   $137.55   $137.50  
  7 purchase totals = $935.44       $1,010.1847   $1,010.19   $1,010.20   $1,010.20