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	$47.71	6.236%	$50.6852	$50.69	$50.70	$50.70
Purchase #2	$173.73	12.543%	$195.521	$195.52	$195.50	$195.50
Purchase #3	$243.51	4.657%	$254.8503	$254.85	$254.85	$254.90
Purchase #4	$160.73	5.520%	$169.6023	$169.60	$169.60	$169.60
Purchase #5	$111.95	5.856%	$118.5058	$118.51	$118.50	$118.50
Purchase #6	$82.26	8.708%	$89.4232	$89.42	$89.40	$89.40
Purchase #7	$89.42	5.779%	$94.5876	$94.59	$94.60	$94.60
7 purchase totals =	$909.31		$973.1754	$973.18	$973.15	$973.20