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 $62.39   11.652%   $69.6597   $69.66   $69.65   $69.70  
  Purchase #2 $173.49   12.757%   $195.6221   $195.62   $195.60   $195.60  
  Purchase #3 $90.74   10.726%   $100.4728   $100.47   $100.45   $100.50  
  Purchase #4 $136.97   10.688%   $151.6094   $151.61   $151.60   $151.60  
  Purchase #5 $132.68   4.847%   $139.111   $139.11   $139.10   $139.10  
  Purchase #6 $8.53   4.262%   $8.8935   $8.89   $8.90   $8.90  
  Purchase #7 $201.40   6.409%   $214.3077   $214.31   $214.30   $214.30  
  7 purchase totals = $806.20       $879.6762   $879.67   $879.60   $879.70