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 $52.44   11.746%   $58.5996   $58.60   $58.60   $58.60  
  Purchase #2 $224.72   9.244%   $245.4931   $245.49   $245.50   $245.50  
  Purchase #3 $219.66   9.525%   $240.5826   $240.58   $240.60   $240.60  
  Purchase #4 $124.61   9.577%   $136.5439   $136.54   $136.55   $136.50  
  Purchase #5 $139.79   7.241%   $149.9122   $149.91   $149.90   $149.90  
  Purchase #6 $240.55   9.158%   $262.5796   $262.58   $262.60   $262.60  
  Purchase #7 $213.90   13.327%   $242.4065   $242.41   $242.40   $242.40  
  7 purchase totals = $1,215.67       $1,336.1175   $1,336.11   $1,336.15   $1,336.10