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	$173.90	8.736%	$189.0919	$189.09	$189.10	$189.10
Purchase #2	$54.82	9.690%	$60.1321	$60.13	$60.15	$60.10
Purchase #3	$53.25	11.340%	$59.2886	$59.29	$59.30	$59.30
Purchase #4	$56.27	10.868%	$62.3854	$62.39	$62.40	$62.40
Purchase #5	$65.91	7.503%	$70.8552	$70.86	$70.85	$70.90
Purchase #6	$167.31	3.481%	$173.1341	$173.13	$173.15	$173.10
Purchase #7	$166.50	5.452%	$175.5776	$175.58	$175.60	$175.60
7 purchase totals =	$737.96		$790.4649	$790.47	$790.55	$790.50