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 $239.83   12.449%   $269.6864   $269.69   $269.70   $269.70  
  Purchase #2 $236.26   6.620%   $251.9004   $251.90   $251.90   $251.90  
  Purchase #3 $148.46   10.219%   $163.6311   $163.63   $163.65   $163.60  
  Purchase #4 $208.86   11.845%   $233.5995   $233.60   $233.60   $233.60  
  Purchase #5 $165.56   11.138%   $184.0001   $184.00   $184.00   $184.00  
  Purchase #6 $31.60   5.567%   $33.3592   $33.36   $33.35   $33.40  
  Purchase #7 $101.27   8.391%   $109.7676   $109.77   $109.75   $109.80  
  7 purchase totals = $1,131.84       $1,245.9443   $1,245.95   $1,245.95   $1,246.00