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	$10.33	5.705%	$10.9193	$10.92	$10.90	$10.90
Purchase #2	$220.40	10.606%	$243.7756	$243.78	$243.80	$243.80
Purchase #3	$34.60	6.423%	$36.8224	$36.82	$36.80	$36.80
Purchase #4	$130.88	10.253%	$144.2991	$144.30	$144.30	$144.30
Purchase #5	$156.49	11.105%	$173.8682	$173.87	$173.85	$173.90
Purchase #6	$191.94	9.557%	$210.2837	$210.28	$210.30	$210.30
Purchase #7	$111.40	6.233%	$118.3436	$118.34	$118.35	$118.30
7 purchase totals =	$856.04		$938.3119	$938.31	$938.30	$938.30