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	$87.89	3.411%	$90.8879	$90.89	$90.90	$90.90
Purchase #2	$248.32	4.110%	$258.526	$258.53	$258.55	$258.50
Purchase #3	$243.92	11.819%	$272.7489	$272.75	$272.75	$272.70
Purchase #4	$203.70	11.621%	$227.372	$227.37	$227.35	$227.40
Purchase #5	$186.78	9.144%	$203.8592	$203.86	$203.85	$203.90
Purchase #6	$186.88	6.716%	$199.4309	$199.43	$199.45	$199.40
Purchase #7	$89.49	3.327%	$92.4673	$92.47	$92.45	$92.50
7 purchase totals =	$1,246.98		$1,345.2922	$1,345.30	$1,345.30	$1,345.30