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	$44.32	13.337%	$50.231	$50.23	$50.25	$50.20
Purchase #2	$165.63	3.737%	$171.8196	$171.82	$171.80	$171.80
Purchase #3	$30.85	8.238%	$33.3914	$33.39	$33.40	$33.40
Purchase #4	$103.31	5.678%	$109.1759	$109.18	$109.20	$109.20
Purchase #5	$157.45	13.230%	$178.2806	$178.28	$178.30	$178.30
Purchase #6	$9.80	8.530%	$10.6359	$10.64	$10.65	$10.60
Purchase #7	$228.91	10.858%	$253.765	$253.77	$253.75	$253.80
7 purchase totals =	$740.27		$807.2994	$807.31	$807.35	$807.30