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	$40.92	13.138%	$46.2961	$46.30	$46.30	$46.30
Purchase #2	$148.52	11.861%	$166.136	$166.14	$166.15	$166.10
Purchase #3	$192.43	8.120%	$208.0553	$208.06	$208.05	$208.10
Purchase #4	$205.78	10.627%	$227.6482	$227.65	$227.65	$227.60
Purchase #5	$100.96	4.724%	$105.7294	$105.73	$105.75	$105.70
Purchase #6	$137.33	11.386%	$152.9664	$152.97	$152.95	$153.00
Purchase #7	$12.52	7.403%	$13.4469	$13.45	$13.45	$13.40
7 purchase totals =	$838.46		$920.2783	$920.30	$920.30	$920.20