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	$206.55	10.658%	$228.5641	$228.56	$228.55	$228.60
Purchase #2	$226.83	3.825%	$235.5062	$235.51	$235.50	$235.50
Purchase #3	$196.73	6.455%	$209.4289	$209.43	$209.45	$209.40
Purchase #4	$185.56	7.277%	$199.0632	$199.06	$199.05	$199.10
Purchase #5	$128.42	12.246%	$144.1463	$144.15	$144.15	$144.10
Purchase #6	$89.35	12.361%	$100.3946	$100.39	$100.40	$100.40
Purchase #7	$11.75	13.164%	$13.2968	$13.30	$13.30	$13.30
7 purchase totals =	$1,045.19		$1,130.4001	$1,130.40	$1,130.40	$1,130.40