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	$7.42	4.863%	$7.7808	$7.78	$7.80	$7.80
Purchase #2	$185.26	3.434%	$191.6218	$191.62	$191.60	$191.60
Purchase #3	$162.33	4.159%	$169.0813	$169.08	$169.10	$169.10
Purchase #4	$44.26	10.309%	$48.8228	$48.82	$48.80	$48.80
Purchase #5	$100.48	7.557%	$108.0733	$108.07	$108.05	$108.10
Purchase #6	$151.85	9.520%	$166.3061	$166.31	$166.30	$166.30
Purchase #7	$35.78	13.126%	$40.4765	$40.48	$40.50	$40.50
7 purchase totals =	$687.38		$732.1626	$732.16	$732.15	$732.20