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	$9.52	13.154%	$10.7723	$10.77	$10.75	$10.80
Purchase #2	$142.62	12.188%	$160.0025	$160.00	$160.00	$160.00
Purchase #3	$51.88	4.183%	$54.0501	$54.05	$54.05	$54.10
Purchase #4	$22.86	8.263%	$24.7489	$24.75	$24.75	$24.70
Purchase #5	$86.59	3.126%	$89.2968	$89.30	$89.30	$89.30
Purchase #6	$210.99	8.471%	$228.863	$228.86	$228.85	$228.90
Purchase #7	$47.69	6.640%	$50.8566	$50.86	$50.85	$50.90
7 purchase totals =	$572.15		$618.5902	$618.59	$618.55	$618.70