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	$52.70	8.320%	$57.0846	$57.08	$57.10	$57.10
Purchase #2	$142.32	8.783%	$154.82	$154.82	$154.80	$154.80
Purchase #3	$70.94	11.725%	$79.2577	$79.26	$79.25	$79.30
Purchase #4	$230.28	8.595%	$250.0726	$250.07	$250.05	$250.10
Purchase #5	$230.88	5.807%	$244.2872	$244.29	$244.30	$244.30
Purchase #6	$113.83	12.336%	$127.8721	$127.87	$127.85	$127.90
Purchase #7	$133.27	10.871%	$147.7578	$147.76	$147.75	$147.80
7 purchase totals =	$974.22		$1,061.1520	$1,061.15	$1,061.10	$1,061.30