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 $86.66   12.617%   $97.5939   $97.59   $97.60   $97.60  
  Purchase #2 $157.36   12.436%   $176.9293   $176.93   $176.95   $176.90  
  Purchase #3 $122.81   3.384%   $126.9659   $126.97   $126.95   $127.00  
  Purchase #4 $120.48   10.535%   $133.1726   $133.17   $133.15   $133.20  
  Purchase #5 $244.25   12.551%   $274.9058   $274.91   $274.90   $274.90  
  Purchase #6 $241.67   8.720%   $262.7436   $262.74   $262.75   $262.70  
  Purchase #7 $129.40   7.698%   $139.3612   $139.36   $139.35   $139.40  
  7 purchase totals = $1,102.63       $1,211.6723   $1,211.67   $1,211.65   $1,211.70