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	$139.54	3.588%	$144.5467	$144.55	$144.55	$144.50
Purchase #2	$149.64	6.189%	$158.9012	$158.90	$158.90	$158.90
Purchase #3	$193.68	3.495%	$200.4491	$200.45	$200.45	$200.40
Purchase #4	$223.77	10.827%	$247.9976	$248.00	$248.00	$248.00
Purchase #5	$198.36	7.337%	$212.9137	$212.91	$212.90	$212.90
Purchase #6	$136.39	11.186%	$151.6466	$151.65	$151.65	$151.60
Purchase #7	$29.90	4.600%	$31.2754	$31.28	$31.30	$31.30
7 purchase totals =	$1,071.28		$1,147.7303	$1,147.74	$1,147.75	$1,147.60