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 $245.48   6.402%   $261.1956   $261.20   $261.20   $261.20  
  Purchase #2 $8.66   7.731%   $9.3295   $9.33   $9.35   $9.30  
  Purchase #3 $200.55   9.828%   $220.2601   $220.26   $220.25   $220.30  
  Purchase #4 $197.49   4.694%   $206.7602   $206.76   $206.75   $206.80  
  Purchase #5 $214.36   4.679%   $224.3899   $224.39   $224.40   $224.40  
  Purchase #6 $231.94   12.728%   $261.4613   $261.46   $261.45   $261.50  
  Purchase #7 $63.42   10.798%   $70.2681   $70.27   $70.25   $70.30  
  7 purchase totals = $1,161.90       $1,253.6647   $1,253.67   $1,253.65   $1,253.80