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	$102.76	13.457%	$116.5884	$116.59	$116.60	$116.60
Purchase #2	$99.26	6.433%	$105.6454	$105.65	$105.65	$105.60
Purchase #3	$180.83	9.825%	$198.5965	$198.60	$198.60	$198.60
Purchase #4	$153.58	11.351%	$171.0129	$171.01	$171.00	$171.00
Purchase #5	$45.67	6.610%	$48.6888	$48.69	$48.70	$48.70
Purchase #6	$40.72	7.498%	$43.7732	$43.77	$43.75	$43.80
Purchase #7	$219.61	13.379%	$248.9916	$248.99	$249.00	$249.00
7 purchase totals =	$842.43		$933.2968	$933.30	$933.30	$933.30