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 $210.71   6.586%   $224.5874   $224.59   $224.60   $224.60  
  Purchase #2 $93.84   4.616%   $98.1717   $98.17   $98.15   $98.20  
  Purchase #3 $215.86   12.371%   $242.564   $242.56   $242.55   $242.60  
  Purchase #4 $48.69   5.433%   $51.3353   $51.34   $51.35   $51.30  
  Purchase #5 $142.92   9.464%   $156.4459   $156.45   $156.45   $156.40  
  Purchase #6 $233.97   8.248%   $253.2678   $253.27   $253.25   $253.30  
  Purchase #7 $118.64   4.686%   $124.1995   $124.20   $124.20   $124.20  
  7 purchase totals = $1,064.63       $1,150.5716   $1,150.58   $1,150.55   $1,150.60