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 $201.49   12.824%   $227.3291   $227.33   $227.35   $227.30  
  Purchase #2 $174.69   12.320%   $196.2118   $196.21   $196.20   $196.20  
  Purchase #3 $197.96   4.752%   $207.3671   $207.37   $207.35   $207.40  
  Purchase #4 $239.28   10.627%   $264.7083   $264.71   $264.70   $264.70  
  Purchase #5 $179.68   9.730%   $197.1629   $197.16   $197.15   $197.20  
  Purchase #6 $214.30   8.853%   $233.272   $233.27   $233.25   $233.30  
  Purchase #7 $22.98   9.176%   $25.0886   $25.09   $25.10   $25.10  
  7 purchase totals = $1,230.38       $1,351.1398   $1,351.14   $1,351.10   $1,351.20