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	$48.43	4.245%	$50.4859	$50.49	$50.50	$50.50
Purchase #2	$73.62	11.584%	$82.1481	$82.15	$82.15	$82.10
Purchase #3	$207.72	11.501%	$231.6099	$231.61	$231.60	$231.60
Purchase #4	$167.62	7.189%	$179.6702	$179.67	$179.65	$179.70
Purchase #5	$92.77	10.191%	$102.2242	$102.22	$102.20	$102.20
Purchase #6	$144.83	5.292%	$152.4944	$152.49	$152.50	$152.50
Purchase #7	$121.87	10.581%	$134.7651	$134.77	$134.75	$134.80
7 purchase totals =	$856.86		$933.3978	$933.40	$933.35	$933.40