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	$39.33	9.874%	$43.2134	$43.21	$43.20	$43.20
Purchase #2	$68.83	4.471%	$71.9074	$71.91	$71.90	$71.90
Purchase #3	$102.42	8.776%	$111.4084	$111.41	$111.40	$111.40
Purchase #4	$244.86	12.565%	$275.6267	$275.63	$275.65	$275.60
Purchase #5	$245.88	10.625%	$272.0048	$272.00	$272.00	$272.00
Purchase #6	$48.60	9.817%	$53.3711	$53.37	$53.35	$53.40
Purchase #7	$145.48	10.627%	$160.9402	$160.94	$160.95	$160.90
7 purchase totals =	$895.40		$988.4720	$988.47	$988.45	$988.40