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	$153.34	6.630%	$163.5064	$163.51	$163.50	$163.50
Purchase #2	$59.44	10.389%	$65.6152	$65.62	$65.60	$65.60
Purchase #3	$188.25	3.536%	$194.9065	$194.91	$194.90	$194.90
Purchase #4	$205.64	5.501%	$216.9523	$216.95	$216.95	$217.00
Purchase #5	$71.63	13.478%	$81.2843	$81.28	$81.30	$81.30
Purchase #6	$36.29	11.254%	$40.3741	$40.37	$40.35	$40.40
Purchase #7	$131.51	4.828%	$137.8593	$137.86	$137.85	$137.90
7 purchase totals =	$846.10		$900.4981	$900.50	$900.45	$900.60