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 $204.91   8.698%   $222.7331   $222.73   $222.75   $222.70  
  Purchase #2 $26.96   10.128%   $29.6905   $29.69   $29.70   $29.70  
  Purchase #3 $6.53   5.732%   $6.9043   $6.90   $6.90   $6.90  
  Purchase #4 $239.67   6.681%   $255.6824   $255.68   $255.70   $255.70  
  Purchase #5 $172.52   13.247%   $195.3737   $195.37   $195.35   $195.40  
  Purchase #6 $233.99   11.215%   $260.232   $260.23   $260.25   $260.20  
  Purchase #7 $153.32   5.485%   $161.7296   $161.73   $161.75   $161.70  
  7 purchase totals = $1,037.90       $1,132.3456   $1,132.33   $1,132.40   $1,132.30