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	$127.31	13.785%	$144.8597	$144.86	$144.85	$144.90
Purchase #2	$40.82	4.510%	$42.661	$42.66	$42.65	$42.70
Purchase #3	$98.78	13.162%	$111.7814	$111.78	$111.80	$111.80
Purchase #4	$203.75	6.643%	$217.2851	$217.29	$217.30	$217.30
Purchase #5	$19.35	12.378%	$21.7451	$21.75	$21.75	$21.70
Purchase #6	$57.92	13.680%	$65.8435	$65.84	$65.85	$65.80
Purchase #7	$234.55	8.107%	$253.565	$253.57	$253.55	$253.60
7 purchase totals =	$782.48		$857.7408	$857.75	$857.75	$857.80