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	$225.66	7.588%	$242.7831	$242.78	$242.80	$242.80
Purchase #2	$88.70	10.762%	$98.2459	$98.25	$98.25	$98.20
Purchase #3	$98.99	12.186%	$111.0529	$111.05	$111.05	$111.10
Purchase #4	$205.33	6.362%	$218.3931	$218.39	$218.40	$218.40
Purchase #5	$149.30	11.367%	$166.2709	$166.27	$166.25	$166.30
Purchase #6	$132.70	8.370%	$143.807	$143.81	$143.80	$143.80
Purchase #7	$172.39	3.437%	$178.315	$178.32	$178.30	$178.30
7 purchase totals =	$1,073.07		$1,158.8679	$1,158.87	$1,158.85	$1,158.90