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 $163.25   13.778%   $185.7426   $185.74   $185.75   $185.70  
  Purchase #2 $190.92   7.201%   $204.6681   $204.67   $204.65   $204.70  
  Purchase #3 $73.61   13.268%   $83.3766   $83.38   $83.40   $83.40  
  Purchase #4 $90.81   7.301%   $97.44   $97.44   $97.45   $97.40  
  Purchase #5 $190.56   9.527%   $208.7147   $208.71   $208.70   $208.70  
  Purchase #6 $249.29   8.103%   $269.49   $269.49   $269.50   $269.50  
  Purchase #7 $215.62   13.335%   $244.3729   $244.37   $244.35   $244.40  
  7 purchase totals = $1,174.06       $1,293.8049   $1,293.80   $1,293.80   $1,293.80