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 $204.44   9.601%   $224.0683   $224.07   $224.05   $224.10  
  Purchase #2 $159.58   10.168%   $175.8061   $175.81   $175.80   $175.80  
  Purchase #3 $7.43   9.503%   $8.1361   $8.14   $8.15   $8.10  
  Purchase #4 $193.76   10.530%   $214.1629   $214.16   $214.15   $214.20  
  Purchase #5 $227.90   5.227%   $239.8123   $239.81   $239.80   $239.80  
  Purchase #6 $212.79   9.813%   $233.6711   $233.67   $233.65   $233.70  
  Purchase #7 $169.66   9.577%   $185.9083   $185.91   $185.90   $185.90  
  7 purchase totals = $1,175.56       $1,281.5651   $1,281.57   $1,281.50   $1,281.60