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	$6.72	12.834%	$7.5824	$7.58	$7.60	$7.60
Purchase #2	$151.59	4.424%	$158.2963	$158.30	$158.30	$158.30
Purchase #3	$57.83	6.335%	$61.4935	$61.49	$61.50	$61.50
Purchase #4	$224.71	10.720%	$248.7989	$248.80	$248.80	$248.80
Purchase #5	$146.35	12.598%	$164.7872	$164.79	$164.80	$164.80
Purchase #6	$46.65	13.595%	$52.9921	$52.99	$53.00	$53.00
Purchase #7	$45.63	3.838%	$47.3813	$47.38	$47.40	$47.40
7 purchase totals =	$679.48		$741.3317	$741.33	$741.40	$741.40