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	$225.31	10.557%	$249.096	$249.10	$249.10	$249.10
Purchase #2	$242.44	13.234%	$274.5245	$274.52	$274.50	$274.50
Purchase #3	$224.63	10.667%	$248.5913	$248.59	$248.60	$248.60
Purchase #4	$137.25	6.719%	$146.4718	$146.47	$146.45	$146.50
Purchase #5	$159.34	3.781%	$165.3646	$165.36	$165.35	$165.40
Purchase #6	$39.69	12.613%	$44.6961	$44.70	$44.70	$44.70
Purchase #7	$238.74	7.193%	$255.9126	$255.91	$255.90	$255.90
7 purchase totals =	$1,267.40		$1,384.6569	$1,384.65	$1,384.60	$1,384.70