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	$89.79	10.437%	$99.1614	$99.16	$99.15	$99.20
Purchase #2	$158.70	9.545%	$173.8479	$173.85	$173.85	$173.80
Purchase #3	$82.32	8.624%	$89.4193	$89.42	$89.40	$89.40
Purchase #4	$148.95	5.517%	$157.1676	$157.17	$157.15	$157.20
Purchase #5	$76.38	12.552%	$85.9672	$85.97	$85.95	$86.00
Purchase #6	$191.41	12.524%	$215.3822	$215.38	$215.40	$215.40
Purchase #7	$144.62	11.105%	$160.6801	$160.68	$160.70	$160.70
7 purchase totals =	$892.17		$981.6257	$981.63	$981.60	$981.70