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	$39.29	9.237%	$42.9192	$42.92	$42.90	$42.90
Purchase #2	$221.95	10.540%	$245.3435	$245.34	$245.35	$245.30
Purchase #3	$62.30	6.328%	$66.2423	$66.24	$66.25	$66.20
Purchase #4	$56.62	5.587%	$59.7834	$59.78	$59.80	$59.80
Purchase #5	$156.30	3.195%	$161.2938	$161.29	$161.30	$161.30
Purchase #6	$137.55	11.376%	$153.1977	$153.20	$153.20	$153.20
Purchase #7	$158.82	8.426%	$172.2022	$172.20	$172.20	$172.20
7 purchase totals =	$832.83		$900.9821	$900.97	$901.00	$900.90