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	$29.29	10.252%	$32.2928	$32.29	$32.30	$32.30
Purchase #2	$111.98	13.131%	$126.6841	$126.68	$126.70	$126.70
Purchase #3	$133.26	13.755%	$151.5899	$151.59	$151.60	$151.60
Purchase #4	$166.67	8.784%	$181.3103	$181.31	$181.30	$181.30
Purchase #5	$146.29	7.263%	$156.915	$156.92	$156.90	$156.90
Purchase #6	$49.81	5.318%	$52.4589	$52.46	$52.45	$52.50
Purchase #7	$135.77	4.811%	$142.3019	$142.30	$142.30	$142.30
7 purchase totals =	$773.07		$843.5529	$843.55	$843.55	$843.60