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	$78.52	5.318%	$82.6957	$82.70	$82.70	$82.70
Purchase #2	$180.84	8.525%	$196.2566	$196.26	$196.25	$196.30
Purchase #3	$11.87	4.740%	$12.4326	$12.43	$12.45	$12.40
Purchase #4	$131.31	10.408%	$144.9767	$144.98	$145.00	$145.00
Purchase #5	$95.78	8.827%	$104.2345	$104.23	$104.25	$104.20
Purchase #6	$156.74	12.666%	$176.5927	$176.59	$176.60	$176.60
Purchase #7	$146.36	7.560%	$157.4248	$157.42	$157.40	$157.40
7 purchase totals =	$801.42		$874.6136	$874.61	$874.65	$874.60