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 $173.62   13.105%   $196.3729   $196.37   $196.35   $196.40  
  Purchase #2 $239.64   9.639%   $262.7389   $262.74   $262.75   $262.70  
  Purchase #3 $233.59   7.723%   $251.6302   $251.63   $251.65   $251.60  
  Purchase #4 $163.30   11.727%   $182.4502   $182.45   $182.45   $182.50  
  Purchase #5 $188.88   12.680%   $212.83   $212.83   $212.85   $212.80  
  Purchase #6 $160.73   7.417%   $172.6513   $172.65   $172.65   $172.70  
  Purchase #7 $64.62   13.160%   $73.124   $73.12   $73.10   $73.10  
  7 purchase totals = $1,224.38       $1,351.7975   $1,351.79   $1,351.80   $1,351.80