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	$82.84	7.492%	$89.0464	$89.05	$89.05	$89.00
Purchase #2	$92.56	11.847%	$103.5256	$103.53	$103.55	$103.50
Purchase #3	$18.99	9.131%	$20.724	$20.72	$20.70	$20.70
Purchase #4	$98.67	13.356%	$111.8484	$111.85	$111.85	$111.80
Purchase #5	$160.31	12.331%	$180.0778	$180.08	$180.10	$180.10
Purchase #6	$243.60	5.376%	$256.6959	$256.70	$256.70	$256.70
Purchase #7	$38.52	6.284%	$40.9406	$40.94	$40.95	$40.90
7 purchase totals =	$735.49		$802.8587	$802.87	$802.90	$802.70