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	$89.74	11.396%	$99.9668	$99.97	$99.95	$100.00
Purchase #2	$114.38	11.624%	$127.6755	$127.68	$127.70	$127.70
Purchase #3	$52.68	9.778%	$57.8311	$57.83	$57.85	$57.80
Purchase #4	$76.59	6.521%	$81.5844	$81.58	$81.60	$81.60
Purchase #5	$12.25	12.874%	$13.8271	$13.83	$13.85	$13.80
Purchase #6	$80.34	3.614%	$83.2435	$83.24	$83.25	$83.20
Purchase #7	$99.26	3.724%	$102.9564	$102.96	$102.95	$103.00
7 purchase totals =	$525.24		$567.0848	$567.09	$567.15	$567.10