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 $181.39   6.204%   $192.6434   $192.64   $192.65   $192.60  
  Purchase #2 $44.26   13.252%   $50.1253   $50.13   $50.15   $50.10  
  Purchase #3 $245.29   9.791%   $269.3063   $269.31   $269.30   $269.30  
  Purchase #4 $86.51   4.209%   $90.1512   $90.15   $90.15   $90.20  
  Purchase #5 $205.42   4.550%   $214.7666   $214.77   $214.75   $214.80  
  Purchase #6 $171.78   13.784%   $195.4582   $195.46   $195.45   $195.50  
  Purchase #7 $204.66   11.177%   $227.5348   $227.53   $227.55   $227.50  
  7 purchase totals = $1,139.31       $1,239.9858   $1,239.99   $1,240.00   $1,240.00