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	$48.39	12.836%	$54.6013	$54.60	$54.60	$54.60
Purchase #2	$140.44	4.569%	$146.8567	$146.86	$146.85	$146.90
Purchase #3	$56.63	9.426%	$61.9679	$61.97	$61.95	$62.00
Purchase #4	$43.62	9.456%	$47.7447	$47.74	$47.75	$47.70
Purchase #5	$149.72	11.440%	$166.848	$166.85	$166.85	$166.80
Purchase #6	$169.71	12.471%	$190.8745	$190.87	$190.85	$190.90
Purchase #7	$196.45	11.733%	$219.4995	$219.50	$219.50	$219.50
7 purchase totals =	$804.96		$888.3926	$888.39	$888.35	$888.40