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 $205.49   13.756%   $233.7572   $233.76   $233.75   $233.80  
  Purchase #2 $61.74   12.337%   $69.3569   $69.36   $69.35   $69.40  
  Purchase #3 $89.85   9.338%   $98.2402   $98.24   $98.25   $98.20  
  Purchase #4 $101.56   4.431%   $106.0601   $106.06   $106.05   $106.10  
  Purchase #5 $222.74   13.795%   $253.467   $253.47   $253.45   $253.50  
  Purchase #6 $90.74   11.863%   $101.5045   $101.50   $101.50   $101.50  
  Purchase #7 $128.29   12.503%   $144.3301   $144.33   $144.35   $144.30  
  7 purchase totals = $900.41       $1,006.7160   $1,006.72   $1,006.70   $1,006.80