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	$44.87	11.727%	$50.1319	$50.13	$50.15	$50.10
Purchase #2	$82.29	13.796%	$93.6427	$93.64	$93.65	$93.60
Purchase #3	$58.28	9.286%	$63.6919	$63.69	$63.70	$63.70
Purchase #4	$204.69	5.290%	$215.5181	$215.52	$215.50	$215.50
Purchase #5	$250.88	13.514%	$284.7839	$284.78	$284.80	$284.80
Purchase #6	$196.52	9.147%	$214.4957	$214.50	$214.50	$214.50
Purchase #7	$54.94	11.590%	$61.3075	$61.31	$61.30	$61.30
7 purchase totals =	$892.47		$983.5717	$983.57	$983.60	$983.50