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 $244.49   8.246%   $264.6506   $264.65   $264.65   $264.70  
  Purchase #2 $189.92   8.187%   $205.4688   $205.47   $205.45   $205.50  
  Purchase #3 $74.49   7.233%   $79.8779   $79.88   $79.90   $79.90  
  Purchase #4 $80.94   3.863%   $84.0667   $84.07   $84.05   $84.10  
  Purchase #5 $58.72   9.386%   $64.2315   $64.23   $64.25   $64.20  
  Purchase #6 $125.80   4.651%   $131.651   $131.65   $131.65   $131.70  
  Purchase #7 $115.76   5.498%   $122.1245   $122.12   $122.10   $122.10  
  7 purchase totals = $890.12       $952.0710   $952.07   $952.05   $952.20