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	$51.42	11.340%	$57.251	$57.25	$57.25	$57.30
Purchase #2	$166.45	5.500%	$175.6048	$175.60	$175.60	$175.60
Purchase #3	$115.79	9.864%	$127.2115	$127.21	$127.20	$127.20
Purchase #4	$27.41	9.800%	$30.0962	$30.10	$30.10	$30.10
Purchase #5	$105.62	5.519%	$111.4492	$111.45	$111.45	$111.40
Purchase #6	$37.38	3.178%	$38.5679	$38.57	$38.55	$38.60
Purchase #7	$235.54	5.414%	$248.2921	$248.29	$248.30	$248.30
7 purchase totals =	$739.61		$788.4727	$788.47	$788.45	$788.50