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	$41.74	9.250%	$45.601	$45.60	$45.60	$45.60
Purchase #2	$121.89	7.593%	$131.1451	$131.15	$131.15	$131.10
Purchase #3	$149.60	6.107%	$158.7361	$158.74	$158.75	$158.70
Purchase #4	$78.87	4.321%	$82.278	$82.28	$82.30	$82.30
Purchase #5	$121.54	13.104%	$137.4666	$137.47	$137.45	$137.50
Purchase #6	$217.43	5.672%	$229.7626	$229.76	$229.75	$229.80
Purchase #7	$149.30	11.629%	$166.6621	$166.66	$166.65	$166.70
7 purchase totals =	$880.37		$951.6515	$951.66	$951.65	$951.70