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	$100.75	10.793%	$111.6239	$111.62	$111.60	$111.60
Purchase #2	$70.53	9.109%	$76.9546	$76.95	$76.95	$77.00
Purchase #3	$111.42	9.768%	$122.3035	$122.30	$122.30	$122.30
Purchase #4	$89.50	5.653%	$94.5594	$94.56	$94.55	$94.60
Purchase #5	$153.98	5.491%	$162.435	$162.44	$162.45	$162.40
Purchase #6	$100.82	11.285%	$112.1975	$112.20	$112.20	$112.20
Purchase #7	$165.38	6.334%	$175.8552	$175.86	$175.85	$175.90
7 purchase totals =	$792.38		$855.9291	$855.93	$855.90	$856.00