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	$34.82	9.280%	$38.0513	$38.05	$38.05	$38.10
Purchase #2	$127.25	9.162%	$138.9086	$138.91	$138.90	$138.90
Purchase #3	$62.86	5.164%	$66.1061	$66.11	$66.10	$66.10
Purchase #4	$242.86	13.242%	$275.0195	$275.02	$275.00	$275.00
Purchase #5	$124.51	3.149%	$128.4308	$128.43	$128.45	$128.40
Purchase #6	$119.57	6.315%	$127.1208	$127.12	$127.10	$127.10
Purchase #7	$47.28	13.408%	$53.6193	$53.62	$53.60	$53.60
7 purchase totals =	$759.15		$827.2564	$827.26	$827.20	$827.20