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	$9.89	9.762%	$10.8555	$10.86	$10.85	$10.90
Purchase #2	$47.59	3.261%	$49.1419	$49.14	$49.15	$49.10
Purchase #3	$13.81	5.743%	$14.6031	$14.60	$14.60	$14.60
Purchase #4	$68.47	7.163%	$73.3745	$73.37	$73.35	$73.40
Purchase #5	$46.89	13.393%	$53.17	$53.17	$53.15	$53.20
Purchase #6	$81.44	11.626%	$90.9082	$90.91	$90.90	$90.90
Purchase #7	$36.63	5.805%	$38.7564	$38.76	$38.75	$38.80
7 purchase totals =	$304.72		$330.8096	$330.81	$330.75	$330.90