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	$108.49	6.591%	$115.6406	$115.64	$115.65	$115.60
Purchase #2	$107.66	5.335%	$113.4037	$113.40	$113.40	$113.40
Purchase #3	$162.66	9.674%	$178.3957	$178.40	$178.40	$178.40
Purchase #4	$90.91	5.114%	$95.5591	$95.56	$95.55	$95.60
Purchase #5	$138.65	4.371%	$144.7104	$144.71	$144.70	$144.70
Purchase #6	$42.25	4.493%	$44.1483	$44.15	$44.15	$44.10
Purchase #7	$104.42	6.744%	$111.4621	$111.46	$111.45	$111.50
7 purchase totals =	$755.04		$803.3199	$803.32	$803.30	$803.30