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	$52.32	10.181%	$57.6467	$57.65	$57.65	$57.60
Purchase #2	$50.30	4.705%	$52.6666	$52.67	$52.65	$52.70
Purchase #3	$117.31	5.200%	$123.4101	$123.41	$123.40	$123.40
Purchase #4	$86.83	8.600%	$94.2974	$94.30	$94.30	$94.30
Purchase #5	$126.78	8.475%	$137.5246	$137.52	$137.50	$137.50
Purchase #6	$235.31	9.120%	$256.7703	$256.77	$256.75	$256.80
Purchase #7	$99.46	6.750%	$106.1736	$106.17	$106.15	$106.20
7 purchase totals =	$768.31		$828.4893	$828.49	$828.40	$828.50