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	$80.72	11.382%	$89.9076	$89.91	$89.90	$89.90
Purchase #2	$59.90	10.611%	$66.256	$66.26	$66.25	$66.30
Purchase #3	$226.68	9.809%	$248.915	$248.92	$248.90	$248.90
Purchase #4	$43.31	5.335%	$45.6206	$45.62	$45.60	$45.60
Purchase #5	$162.74	6.727%	$173.6875	$173.69	$173.70	$173.70
Purchase #6	$19.99	3.510%	$20.6916	$20.69	$20.70	$20.70
Purchase #7	$139.67	10.654%	$154.5504	$154.55	$154.55	$154.60
7 purchase totals =	$733.01		$799.6287	$799.64	$799.60	$799.70