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 $182.28   11.610%   $203.4427   $203.44   $203.45   $203.40  
  Purchase #2 $218.97   10.184%   $241.2699   $241.27   $241.25   $241.30  
  Purchase #3 $18.78   9.396%   $20.5446   $20.54   $20.55   $20.50  
  Purchase #4 $144.25   10.462%   $159.3414   $159.34   $159.35   $159.30  
  Purchase #5 $239.71   3.216%   $247.4191   $247.42   $247.40   $247.40  
  Purchase #6 $133.37   6.559%   $142.1177   $142.12   $142.10   $142.10  
  Purchase #7 $46.71   5.275%   $49.174   $49.17   $49.15   $49.20  
  7 purchase totals = $984.07       $1,063.3094   $1,063.30   $1,063.25   $1,063.20