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	$74.39	4.227%	$77.5345	$77.53	$77.55	$77.50
Purchase #2	$137.75	13.819%	$156.7857	$156.79	$156.80	$156.80
Purchase #3	$138.28	10.740%	$153.1313	$153.13	$153.15	$153.10
Purchase #4	$91.84	4.275%	$95.7662	$95.77	$95.75	$95.80
Purchase #5	$226.42	10.845%	$250.9752	$250.98	$251.00	$251.00
Purchase #6	$173.96	12.823%	$196.2669	$196.27	$196.25	$196.30
Purchase #7	$129.79	12.132%	$145.5361	$145.54	$145.55	$145.50
7 purchase totals =	$972.43		$1,075.9959	$1,076.01	$1,076.05	$1,076.00