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	$20.26	11.826%	$22.6559	$22.66	$22.65	$22.70
Purchase #2	$153.36	6.494%	$163.3192	$163.32	$163.30	$163.30
Purchase #3	$196.28	12.152%	$220.1319	$220.13	$220.15	$220.10
Purchase #4	$145.29	5.586%	$153.4059	$153.41	$153.40	$153.40
Purchase #5	$74.86	10.672%	$82.8491	$82.85	$82.85	$82.80
Purchase #6	$80.64	11.518%	$89.9281	$89.93	$89.95	$89.90
Purchase #7	$151.87	9.690%	$166.5862	$166.59	$166.60	$166.60
7 purchase totals =	$822.56		$898.8763	$898.89	$898.90	$898.80