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 $68.66   6.468%   $73.1009   $73.10   $73.10   $73.10  
  Purchase #2 $219.26   5.406%   $231.1132   $231.11   $231.10   $231.10  
  Purchase #3 $173.58   10.856%   $192.4238   $192.42   $192.40   $192.40  
  Purchase #4 $208.69   3.394%   $215.7729   $215.77   $215.75   $215.80  
  Purchase #5 $199.75   5.556%   $210.8481   $210.85   $210.85   $210.80  
  Purchase #6 $119.75   11.410%   $133.4135   $133.41   $133.40   $133.40  
  Purchase #7 $167.70   9.249%   $183.2106   $183.21   $183.20   $183.20  
  7 purchase totals = $1,157.39       $1,239.8830   $1,239.87   $1,239.80   $1,239.80