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 $60.75   10.520%   $67.1409   $67.14   $67.15   $67.10  
  Purchase #2 $186.93   7.706%   $201.3348   $201.33   $201.35   $201.30  
  Purchase #3 $239.69   9.564%   $262.614   $262.61   $262.60   $262.60  
  Purchase #4 $187.44   12.467%   $210.8081   $210.81   $210.80   $210.80  
  Purchase #5 $13.88   13.143%   $15.7042   $15.70   $15.70   $15.70  
  Purchase #6 $247.87   11.608%   $276.6427   $276.64   $276.65   $276.60  
  Purchase #7 $194.60   5.391%   $205.0909   $205.09   $205.10   $205.10  
  7 purchase totals = $1,131.16       $1,239.3356   $1,239.32   $1,239.35   $1,239.20