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	$136.44	5.683%	$144.1939	$144.19	$144.20	$144.20
Purchase #2	$16.31	5.147%	$17.1495	$17.15	$17.15	$17.10
Purchase #3	$71.45	12.695%	$80.5206	$80.52	$80.50	$80.50
Purchase #4	$226.62	10.460%	$250.3245	$250.32	$250.30	$250.30
Purchase #5	$52.98	3.538%	$54.8544	$54.85	$54.85	$54.90
Purchase #6	$61.32	10.472%	$67.7414	$67.74	$67.75	$67.70
Purchase #7	$151.51	10.797%	$167.8685	$167.87	$167.85	$167.90
7 purchase totals =	$716.63		$782.6528	$782.64	$782.60	$782.60