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	$204.84	11.734%	$228.8759	$228.88	$228.90	$228.90
Purchase #2	$157.52	9.572%	$172.5978	$172.60	$172.60	$172.60
Purchase #3	$193.78	9.243%	$211.6911	$211.69	$211.70	$211.70
Purchase #4	$117.84	11.778%	$131.7192	$131.72	$131.70	$131.70
Purchase #5	$152.37	13.750%	$173.3209	$173.32	$173.30	$173.30
Purchase #6	$101.94	12.223%	$114.4001	$114.40	$114.40	$114.40
Purchase #7	$173.34	9.208%	$189.3011	$189.30	$189.30	$189.30
7 purchase totals =	$1,101.63		$1,221.9061	$1,221.91	$1,221.90	$1,221.90