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	$16.31	8.324%	$17.6676	$17.67	$17.65	$17.70
Purchase #2	$68.39	5.604%	$72.2226	$72.22	$72.20	$72.20
Purchase #3	$239.84	6.122%	$254.523	$254.52	$254.50	$254.50
Purchase #4	$146.25	6.853%	$156.2725	$156.27	$156.25	$156.30
Purchase #5	$9.25	13.620%	$10.5099	$10.51	$10.50	$10.50
Purchase #6	$96.49	3.332%	$99.705	$99.71	$99.70	$99.70
Purchase #7	$44.80	10.694%	$49.5909	$49.59	$49.60	$49.60
7 purchase totals =	$621.33		$660.4915	$660.49	$660.40	$660.50