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 $243.61   4.271%   $254.0146   $254.01   $254.00   $254.00  
  Purchase #2 $183.86   13.526%   $208.7289   $208.73   $208.75   $208.70  
  Purchase #3 $163.50   13.569%   $185.6853   $185.69   $185.70   $185.70  
  Purchase #4 $250.85   3.579%   $259.8279   $259.83   $259.85   $259.80  
  Purchase #5 $200.32   7.805%   $215.955   $215.96   $215.95   $216.00  
  Purchase #6 $128.86   3.145%   $132.9126   $132.91   $132.90   $132.90  
  Purchase #7 $9.94   5.702%   $10.5068   $10.51   $10.50   $10.50  
  7 purchase totals = $1,180.94       $1,267.6311   $1,267.64   $1,267.65   $1,267.60