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	$54.91	4.734%	$57.5094	$57.51	$57.50	$57.50
Purchase #2	$115.94	13.735%	$131.8644	$131.86	$131.85	$131.90
Purchase #3	$125.95	4.580%	$131.7185	$131.72	$131.70	$131.70
Purchase #4	$112.29	12.304%	$126.1062	$126.11	$126.10	$126.10
Purchase #5	$106.28	10.615%	$117.5616	$117.56	$117.55	$117.60
Purchase #6	$30.58	8.651%	$33.2255	$33.23	$33.25	$33.20
Purchase #7	$36.31	13.315%	$41.1447	$41.14	$41.15	$41.10
7 purchase totals =	$582.26		$639.1303	$639.13	$639.10	$639.10