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	$139.85	13.590%	$158.8556	$158.86	$158.85	$158.90
Purchase #2	$25.26	9.643%	$27.6958	$27.70	$27.70	$27.70
Purchase #3	$53.25	5.396%	$56.1234	$56.12	$56.10	$56.10
Purchase #4	$88.68	13.654%	$100.7884	$100.79	$100.80	$100.80
Purchase #5	$103.90	7.308%	$111.493	$111.49	$111.50	$111.50
Purchase #6	$213.41	9.220%	$233.0864	$233.09	$233.10	$233.10
Purchase #7	$75.48	5.783%	$79.845	$79.85	$79.85	$79.80
7 purchase totals =	$699.83		$767.8876	$767.90	$767.90	$767.90