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	$155.37	11.861%	$173.7984	$173.80	$173.80	$173.80
Purchase #2	$136.75	6.440%	$145.5567	$145.56	$145.55	$145.60
Purchase #3	$30.83	4.338%	$32.1674	$32.17	$32.15	$32.20
Purchase #4	$166.74	4.727%	$174.6218	$174.62	$174.60	$174.60
Purchase #5	$227.84	4.586%	$238.2887	$238.29	$238.30	$238.30
Purchase #6	$30.65	9.138%	$33.4508	$33.45	$33.45	$33.50
Purchase #7	$84.94	5.802%	$89.8682	$89.87	$89.85	$89.90
7 purchase totals =	$833.12		$887.7520	$887.76	$887.70	$887.90