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	$69.91	10.182%	$77.0282	$77.03	$77.05	$77.00
Purchase #2	$173.92	6.537%	$185.2892	$185.29	$185.30	$185.30
Purchase #3	$40.31	5.463%	$42.5121	$42.51	$42.50	$42.50
Purchase #4	$36.86	11.378%	$41.0539	$41.05	$41.05	$41.10
Purchase #5	$106.29	6.190%	$112.8694	$112.87	$112.85	$112.90
Purchase #6	$233.49	10.280%	$257.4928	$257.49	$257.50	$257.50
Purchase #7	$144.92	9.589%	$158.8164	$158.82	$158.80	$158.80
7 purchase totals =	$805.70		$875.0620	$875.06	$875.05	$875.10