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 $233.31   12.868%   $263.3323   $263.33   $263.35   $263.30  
  Purchase #2 $197.62   3.680%   $204.8924   $204.89   $204.90   $204.90  
  Purchase #3 $222.47   4.503%   $232.4878   $232.49   $232.50   $232.50  
  Purchase #4 $106.77   8.597%   $115.949   $115.95   $115.95   $115.90  
  Purchase #5 $164.61   6.457%   $175.2389   $175.24   $175.25   $175.20  
  Purchase #6 $85.81   3.294%   $88.6366   $88.64   $88.65   $88.60  
  Purchase #7 $168.41   5.836%   $178.2384   $178.24   $178.25   $178.20  
  7 purchase totals = $1,179.00       $1,258.7754   $1,258.78   $1,258.85   $1,258.60