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	$141.65	3.440%	$146.5228	$146.52	$146.50	$146.50
Purchase #2	$78.81	8.760%	$85.7138	$85.71	$85.70	$85.70
Purchase #3	$52.49	4.311%	$54.7528	$54.75	$54.75	$54.80
Purchase #4	$191.25	13.779%	$217.6023	$217.60	$217.60	$217.60
Purchase #5	$117.86	10.732%	$130.5087	$130.51	$130.50	$130.50
Purchase #6	$54.27	3.543%	$56.1928	$56.19	$56.20	$56.20
Purchase #7	$99.86	6.394%	$106.245	$106.25	$106.25	$106.20
7 purchase totals =	$736.19		$797.5382	$797.53	$797.50	$797.50