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	$165.91	10.471%	$183.2824	$183.28	$183.30	$183.30
Purchase #2	$127.65	9.296%	$139.5163	$139.52	$139.50	$139.50
Purchase #3	$83.45	13.451%	$94.6749	$94.67	$94.65	$94.70
Purchase #4	$36.79	13.417%	$41.7261	$41.73	$41.75	$41.70
Purchase #5	$106.41	4.463%	$111.1591	$111.16	$111.15	$111.20
Purchase #6	$238.59	7.380%	$256.1979	$256.20	$256.20	$256.20
Purchase #7	$102.75	10.341%	$113.3754	$113.38	$113.40	$113.40
7 purchase totals =	$861.55		$939.9321	$939.94	$939.95	$940.00