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 $23.97   10.429%   $26.4698   $26.47   $26.45   $26.50  
  Purchase #2 $94.78   6.248%   $100.7019   $100.70   $100.70   $100.70  
  Purchase #3 $58.75   3.140%   $60.5948   $60.59   $60.60   $60.60  
  Purchase #4 $172.87   6.130%   $183.4669   $183.47   $183.45   $183.50  
  Purchase #5 $57.73   10.220%   $63.63   $63.63   $63.65   $63.60  
  Purchase #6 $52.91   6.374%   $56.2825   $56.28   $56.30   $56.30  
  Purchase #7 $131.62   7.279%   $141.2006   $141.20   $141.20   $141.20  
  7 purchase totals = $592.63       $632.3465   $632.34   $632.35   $632.40