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	$93.80	6.826%	$100.2028	$100.20	$100.20	$100.20
Purchase #2	$155.45	8.277%	$168.3166	$168.32	$168.30	$168.30
Purchase #3	$153.49	8.442%	$166.4476	$166.45	$166.45	$166.40
Purchase #4	$199.40	4.564%	$208.5006	$208.50	$208.50	$208.50
Purchase #5	$80.97	11.619%	$90.3779	$90.38	$90.40	$90.40
Purchase #6	$129.79	5.273%	$136.6338	$136.63	$136.65	$136.60
Purchase #7	$204.73	11.757%	$228.8001	$228.80	$228.80	$228.80
7 purchase totals =	$1,017.63		$1,099.2794	$1,099.28	$1,099.30	$1,099.20