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	$89.55	12.699%	$100.922	$100.92	$100.90	$100.90
Purchase #2	$58.65	4.478%	$61.2763	$61.28	$61.30	$61.30
Purchase #3	$151.71	8.112%	$164.0167	$164.02	$164.00	$164.00
Purchase #4	$113.26	8.167%	$122.5099	$122.51	$122.50	$122.50
Purchase #5	$98.79	13.167%	$111.7977	$111.80	$111.80	$111.80
Purchase #6	$132.43	10.110%	$145.8187	$145.82	$145.80	$145.80
Purchase #7	$8.37	5.460%	$8.827	$8.83	$8.85	$8.80
7 purchase totals =	$652.76		$715.1683	$715.18	$715.15	$715.10