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	$74.28	5.847%	$78.6232	$78.62	$78.60	$78.60
Purchase #2	$233.39	12.149%	$261.7446	$261.74	$261.75	$261.70
Purchase #3	$126.92	10.490%	$140.2339	$140.23	$140.25	$140.20
Purchase #4	$170.47	6.283%	$181.1806	$181.18	$181.20	$181.20
Purchase #5	$103.46	7.351%	$111.0653	$111.07	$111.05	$111.10
Purchase #6	$157.32	3.354%	$162.5965	$162.60	$162.60	$162.60
Purchase #7	$105.99	12.644%	$119.3914	$119.39	$119.40	$119.40
7 purchase totals =	$971.83		$1,054.8355	$1,054.83	$1,054.85	$1,054.80