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	$179.52	11.821%	$200.7411	$200.74	$200.75	$200.70
Purchase #2	$107.66	10.415%	$118.8728	$118.87	$118.85	$118.90
Purchase #3	$211.40	7.292%	$226.8153	$226.82	$226.80	$226.80
Purchase #4	$42.67	12.191%	$47.8719	$47.87	$47.85	$47.90
Purchase #5	$161.28	3.118%	$166.3087	$166.31	$166.30	$166.30
Purchase #6	$105.72	5.724%	$111.7714	$111.77	$111.75	$111.80
Purchase #7	$201.28	12.787%	$227.0177	$227.02	$227.00	$227.00
7 purchase totals =	$1,009.53		$1,099.3989	$1,099.40	$1,099.30	$1,099.40