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	$242.27	13.220%	$274.2981	$274.30	$274.30	$274.30
Purchase #2	$183.51	5.795%	$194.1444	$194.14	$194.15	$194.10
Purchase #3	$218.75	6.751%	$233.5178	$233.52	$233.50	$233.50
Purchase #4	$42.31	4.666%	$44.2842	$44.28	$44.30	$44.30
Purchase #5	$196.56	9.834%	$215.8897	$215.89	$215.90	$215.90
Purchase #6	$158.99	12.211%	$178.4043	$178.40	$178.40	$178.40
Purchase #7	$46.58	3.209%	$48.0748	$48.07	$48.05	$48.10
7 purchase totals =	$1,088.97		$1,188.6133	$1,188.60	$1,188.60	$1,188.60