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	$116.51	3.505%	$120.5937	$120.59	$120.60	$120.60
Purchase #2	$140.83	12.823%	$158.8886	$158.89	$158.90	$158.90
Purchase #3	$56.74	8.179%	$61.3808	$61.38	$61.40	$61.40
Purchase #4	$219.37	5.309%	$231.0164	$231.02	$231.00	$231.00
Purchase #5	$57.72	10.367%	$63.7038	$63.70	$63.70	$63.70
Purchase #6	$37.86	10.589%	$41.869	$41.87	$41.85	$41.90
Purchase #7	$54.93	10.405%	$60.6455	$60.65	$60.65	$60.60
7 purchase totals =	$683.96		$738.0978	$738.10	$738.10	$738.10