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	$35.46	6.309%	$37.6972	$37.70	$37.70	$37.70
Purchase #2	$202.91	7.248%	$217.6169	$217.62	$217.60	$217.60
Purchase #3	$113.51	12.795%	$128.0336	$128.03	$128.05	$128.00
Purchase #4	$131.83	9.677%	$144.5872	$144.59	$144.60	$144.60
Purchase #5	$96.49	9.614%	$105.7665	$105.77	$105.75	$105.80
Purchase #6	$81.64	10.276%	$90.0293	$90.03	$90.05	$90.00
Purchase #7	$173.80	4.624%	$181.8365	$181.84	$181.85	$181.80
7 purchase totals =	$835.64		$905.5672	$905.58	$905.60	$905.50