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	$33.55	10.341%	$37.0194	$37.02	$37.00	$37.00
Purchase #2	$110.83	9.242%	$121.0729	$121.07	$121.05	$121.10
Purchase #3	$141.77	8.247%	$153.4618	$153.46	$153.45	$153.50
Purchase #4	$39.28	9.783%	$43.1228	$43.12	$43.10	$43.10
Purchase #5	$244.64	6.394%	$260.2823	$260.28	$260.30	$260.30
Purchase #6	$46.91	7.588%	$50.4695	$50.47	$50.45	$50.50
Purchase #7	$98.29	13.869%	$111.9218	$111.92	$111.90	$111.90
7 purchase totals =	$715.27		$777.3505	$777.34	$777.25	$777.40