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	$210.31	13.351%	$238.3885	$238.39	$238.40	$238.40
Purchase #2	$79.25	11.785%	$88.5896	$88.59	$88.60	$88.60
Purchase #3	$223.82	7.845%	$241.3787	$241.38	$241.40	$241.40
Purchase #4	$230.93	3.201%	$238.3221	$238.32	$238.30	$238.30
Purchase #5	$51.33	5.298%	$54.0495	$54.05	$54.05	$54.00
Purchase #6	$219.50	10.379%	$242.2819	$242.28	$242.30	$242.30
Purchase #7	$47.96	13.801%	$54.579	$54.58	$54.60	$54.60
7 purchase totals =	$1,063.10		$1,157.5893	$1,157.59	$1,157.65	$1,157.60