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	$101.65	9.814%	$111.6259	$111.63	$111.65	$111.60
Purchase #2	$73.92	13.181%	$83.6634	$83.66	$83.65	$83.70
Purchase #3	$10.80	7.218%	$11.5795	$11.58	$11.60	$11.60
Purchase #4	$51.91	4.819%	$54.4115	$54.41	$54.40	$54.40
Purchase #5	$28.44	11.481%	$31.7052	$31.71	$31.70	$31.70
Purchase #6	$132.81	9.529%	$145.4655	$145.47	$145.45	$145.50
Purchase #7	$158.73	6.645%	$169.2776	$169.28	$169.30	$169.30
7 purchase totals =	$558.26		$607.7286	$607.74	$607.75	$607.80