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 $59.29   7.786%   $63.9063   $63.91   $63.90   $63.90  
  Purchase #2 $106.85   8.492%   $115.9237   $115.92   $115.90   $115.90  
  Purchase #3 $117.96   13.440%   $133.8138   $133.81   $133.80   $133.80  
  Purchase #4 $5.94   11.392%   $6.6167   $6.62   $6.60   $6.60  
  Purchase #5 $204.29   5.544%   $215.6158   $215.62   $215.60   $215.60  
  Purchase #6 $166.64   11.756%   $186.2302   $186.23   $186.25   $186.20  
  Purchase #7 $6.70   4.655%   $7.0119   $7.01   $7.00   $7.00  
  7 purchase totals = $667.67       $729.1184   $729.12   $729.05   $729.00