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	$166.99	5.665%	$176.45	$176.45	$176.45	$176.50
Purchase #2	$221.44	13.452%	$251.2281	$251.23	$251.25	$251.20
Purchase #3	$107.85	6.502%	$114.8624	$114.86	$114.85	$114.90
Purchase #4	$17.66	4.493%	$18.4535	$18.45	$18.45	$18.50
Purchase #5	$75.26	9.114%	$82.1192	$82.12	$82.10	$82.10
Purchase #6	$73.94	11.805%	$82.6686	$82.67	$82.65	$82.70
Purchase #7	$56.56	9.194%	$61.7601	$61.76	$61.75	$61.80
7 purchase totals =	$719.70		$787.5419	$787.54	$787.50	$787.70