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	$51.93	10.814%	$57.5457	$57.55	$57.55	$57.50
Purchase #2	$37.52	4.567%	$39.2335	$39.23	$39.25	$39.20
Purchase #3	$113.29	9.564%	$124.1251	$124.13	$124.15	$124.10
Purchase #4	$85.70	3.197%	$88.4398	$88.44	$88.45	$88.40
Purchase #5	$47.88	9.846%	$52.5943	$52.59	$52.60	$52.60
Purchase #6	$97.75	6.142%	$103.7538	$103.75	$103.75	$103.80
Purchase #7	$134.66	12.548%	$151.5571	$151.56	$151.55	$151.60
7 purchase totals =	$568.73		$617.2493	$617.25	$617.30	$617.20