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	$37.38	13.689%	$42.4969	$42.50	$42.50	$42.50
Purchase #2	$11.95	13.383%	$13.5493	$13.55	$13.55	$13.50
Purchase #3	$137.87	9.482%	$150.9428	$150.94	$150.95	$150.90
Purchase #4	$200.31	10.335%	$221.012	$221.01	$221.00	$221.00
Purchase #5	$187.83	11.475%	$209.3835	$209.38	$209.40	$209.40
Purchase #6	$238.40	9.286%	$260.5378	$260.54	$260.55	$260.50
Purchase #7	$236.66	13.188%	$267.8707	$267.87	$267.85	$267.90
7 purchase totals =	$1,050.40		$1,165.7930	$1,165.79	$1,165.80	$1,165.70