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	$47.85	8.838%	$52.079	$52.08	$52.10	$52.10
Purchase #2	$17.97	13.725%	$20.4364	$20.44	$20.45	$20.40
Purchase #3	$43.71	12.808%	$49.3084	$49.31	$49.30	$49.30
Purchase #4	$217.54	11.377%	$242.2895	$242.29	$242.30	$242.30
Purchase #5	$95.84	4.565%	$100.2151	$100.22	$100.20	$100.20
Purchase #6	$100.89	12.403%	$113.4034	$113.40	$113.40	$113.40
Purchase #7	$59.46	13.143%	$67.2748	$67.27	$67.25	$67.30
7 purchase totals =	$583.26		$645.0066	$645.01	$645.00	$645.00