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	$21.27	11.103%	$23.6316	$23.63	$23.65	$23.60
Purchase #2	$178.41	12.438%	$200.6006	$200.60	$200.60	$200.60
Purchase #3	$174.51	9.247%	$190.6469	$190.65	$190.65	$190.60
Purchase #4	$137.82	11.673%	$153.9077	$153.91	$153.90	$153.90
Purchase #5	$128.85	7.393%	$138.3759	$138.38	$138.40	$138.40
Purchase #6	$18.56	11.562%	$20.7059	$20.71	$20.70	$20.70
Purchase #7	$86.45	4.445%	$90.2927	$90.29	$90.30	$90.30
7 purchase totals =	$745.87		$818.1613	$818.17	$818.20	$818.10