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	$173.30	5.748%	$183.2613	$183.26	$183.25	$183.30
Purchase #2	$40.92	12.776%	$46.1479	$46.15	$46.15	$46.10
Purchase #3	$136.88	9.248%	$149.5387	$149.54	$149.55	$149.50
Purchase #4	$91.37	7.723%	$98.4265	$98.43	$98.45	$98.40
Purchase #5	$107.79	3.277%	$111.3223	$111.32	$111.30	$111.30
Purchase #6	$57.49	11.476%	$64.0876	$64.09	$64.10	$64.10
Purchase #7	$51.32	6.382%	$54.5952	$54.60	$54.60	$54.60
7 purchase totals =	$659.07		$707.3795	$707.39	$707.40	$707.30