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 $60.80   4.232%   $63.3731   $63.37   $63.35   $63.40  
  Purchase #2 $84.97   12.790%   $95.8377   $95.84   $95.85   $95.80  
  Purchase #3 $158.79   4.212%   $165.4782   $165.48   $165.50   $165.50  
  Purchase #4 $76.42   12.183%   $85.7302   $85.73   $85.75   $85.70  
  Purchase #5 $127.83   7.175%   $137.0018   $137.00   $137.00   $137.00  
  Purchase #6 $108.81   8.161%   $117.69   $117.69   $117.70   $117.70  
  Purchase #7 $115.41   3.856%   $119.8602   $119.86   $119.85   $119.90  
  7 purchase totals = $733.03       $784.9712   $784.97   $785.00   $785.00