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	$233.62	3.823%	$242.5513	$242.55	$242.55	$242.60
Purchase #2	$81.68	10.586%	$90.3266	$90.33	$90.35	$90.30
Purchase #3	$166.32	8.321%	$180.1595	$180.16	$180.15	$180.20
Purchase #4	$230.72	3.299%	$238.3315	$238.33	$238.35	$238.30
Purchase #5	$237.32	10.583%	$262.4356	$262.44	$262.45	$262.40
Purchase #6	$182.30	4.742%	$190.9447	$190.94	$190.95	$190.90
Purchase #7	$108.64	9.486%	$118.9456	$118.95	$118.95	$118.90
7 purchase totals =	$1,240.60		$1,323.6948	$1,323.70	$1,323.75	$1,323.60