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	$26.67	5.700%	$28.1902	$28.19	$28.20	$28.20
Purchase #2	$153.46	12.560%	$172.7346	$172.73	$172.75	$172.70
Purchase #3	$111.51	8.440%	$120.9214	$120.92	$120.90	$120.90
Purchase #4	$46.88	5.861%	$49.6276	$49.63	$49.65	$49.60
Purchase #5	$130.27	9.404%	$142.5206	$142.52	$142.50	$142.50
Purchase #6	$33.53	13.147%	$37.9382	$37.94	$37.95	$37.90
Purchase #7	$87.61	7.600%	$94.2684	$94.27	$94.25	$94.30
7 purchase totals =	$589.93		$646.2010	$646.20	$646.20	$646.10