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	$175.50	13.510%	$199.2101	$199.21	$199.20	$199.20
Purchase #2	$220.89	4.838%	$231.5767	$231.58	$231.60	$231.60
Purchase #3	$74.98	6.506%	$79.8582	$79.86	$79.85	$79.90
Purchase #4	$39.69	9.411%	$43.4252	$43.43	$43.45	$43.40
Purchase #5	$31.91	4.722%	$33.4168	$33.42	$33.40	$33.40
Purchase #6	$37.87	4.370%	$39.5249	$39.52	$39.50	$39.50
Purchase #7	$142.35	6.522%	$151.6341	$151.63	$151.65	$151.60
7 purchase totals =	$723.19		$778.6460	$778.65	$778.65	$778.60