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 $248.44   12.183%   $278.7074   $278.71   $278.70   $278.70  
  Purchase #2 $56.55   10.744%   $62.6257   $62.63   $62.65   $62.60  
  Purchase #3 $24.69   11.179%   $27.4501   $27.45   $27.45   $27.50  
  Purchase #4 $208.44   6.235%   $221.4362   $221.44   $221.45   $221.40  
  Purchase #5 $129.48   3.818%   $134.4235   $134.42   $134.40   $134.40  
  Purchase #6 $195.81   7.571%   $210.6348   $210.63   $210.65   $210.60  
  Purchase #7 $71.29   11.117%   $79.2153   $79.22   $79.20   $79.20  
  7 purchase totals = $934.70       $1,014.4930   $1,014.50   $1,014.50   $1,014.40