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	$162.27	9.855%	$178.2617	$178.26	$178.25	$178.30
Purchase #2	$132.42	3.169%	$136.6164	$136.62	$136.60	$136.60
Purchase #3	$54.91	8.122%	$59.3698	$59.37	$59.35	$59.40
Purchase #4	$236.58	12.381%	$265.871	$265.87	$265.85	$265.90
Purchase #5	$71.45	9.708%	$78.3864	$78.39	$78.40	$78.40
Purchase #6	$18.28	10.539%	$20.2065	$20.21	$20.20	$20.20
Purchase #7	$105.81	5.187%	$111.2984	$111.30	$111.30	$111.30
7 purchase totals =	$781.72		$850.0102	$850.02	$849.95	$850.10