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 $120.27   3.247%   $124.1752   $124.18   $124.20   $124.20  
  Purchase #2 $250.95   12.617%   $282.6124   $282.61   $282.60   $282.60  
  Purchase #3 $154.47   5.789%   $163.4123   $163.41   $163.40   $163.40  
  Purchase #4 $249.31   13.874%   $283.8993   $283.90   $283.90   $283.90  
  Purchase #5 $53.69   6.852%   $57.3688   $57.37   $57.35   $57.40  
  Purchase #6 $186.67   6.665%   $199.1116   $199.11   $199.10   $199.10  
  Purchase #7 $154.91   6.299%   $164.6678   $164.67   $164.65   $164.70  
  7 purchase totals = $1,170.27       $1,275.2474   $1,275.25   $1,275.20   $1,275.30