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	$105.28	3.163%	$108.61	$108.61	$108.60	$108.60
Purchase #2	$146.72	13.114%	$165.9609	$165.96	$165.95	$166.00
Purchase #3	$102.52	8.281%	$111.0097	$111.01	$111.00	$111.00
Purchase #4	$165.67	6.724%	$176.8097	$176.81	$176.80	$176.80
Purchase #5	$81.79	13.651%	$92.9552	$92.96	$92.95	$93.00
Purchase #6	$98.72	9.120%	$107.7233	$107.72	$107.70	$107.70
Purchase #7	$30.62	10.727%	$33.9046	$33.90	$33.90	$33.90
7 purchase totals =	$731.32		$796.9734	$796.97	$796.90	$797.00