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	$109.32	4.201%	$113.9125	$113.91	$113.90	$113.90
Purchase #2	$71.85	8.262%	$77.7862	$77.79	$77.80	$77.80
Purchase #3	$223.78	8.350%	$242.4656	$242.47	$242.45	$242.50
Purchase #4	$113.71	11.739%	$127.0584	$127.06	$127.05	$127.10
Purchase #5	$72.39	12.738%	$81.611	$81.61	$81.60	$81.60
Purchase #6	$205.58	7.519%	$221.0376	$221.04	$221.05	$221.00
Purchase #7	$43.28	11.629%	$48.313	$48.31	$48.30	$48.30
7 purchase totals =	$839.91		$912.1843	$912.19	$912.15	$912.20