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	$119.51	6.502%	$127.2805	$127.28	$127.30	$127.30
Purchase #2	$197.89	3.273%	$204.3669	$204.37	$204.35	$204.40
Purchase #3	$156.99	10.640%	$173.6937	$173.69	$173.70	$173.70
Purchase #4	$63.56	13.508%	$72.1457	$72.15	$72.15	$72.10
Purchase #5	$131.46	11.244%	$146.2414	$146.24	$146.25	$146.20
Purchase #6	$93.38	5.557%	$98.5691	$98.57	$98.55	$98.60
Purchase #7	$78.99	11.597%	$88.1505	$88.15	$88.15	$88.20
7 purchase totals =	$841.78		$910.4478	$910.45	$910.45	$910.50