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	$35.68	10.531%	$39.4375	$39.44	$39.45	$39.40
Purchase #2	$173.69	5.550%	$183.3298	$183.33	$183.35	$183.30
Purchase #3	$5.55	12.415%	$6.239	$6.24	$6.25	$6.20
Purchase #4	$89.89	11.559%	$100.2804	$100.28	$100.30	$100.30
Purchase #5	$6.92	8.446%	$7.5045	$7.50	$7.50	$7.50
Purchase #6	$47.55	9.826%	$52.2223	$52.22	$52.20	$52.20
Purchase #7	$158.66	13.162%	$179.5428	$179.54	$179.55	$179.50
7 purchase totals =	$517.94		$568.5563	$568.55	$568.60	$568.40