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	$21.85	10.839%	$24.2183	$24.22	$24.20	$24.20
Purchase #2	$244.59	9.814%	$268.5941	$268.59	$268.60	$268.60
Purchase #3	$40.95	13.564%	$46.5045	$46.50	$46.50	$46.50
Purchase #4	$113.73	11.195%	$126.4621	$126.46	$126.45	$126.50
Purchase #5	$45.38	13.671%	$51.5839	$51.58	$51.60	$51.60
Purchase #6	$80.50	11.146%	$89.4725	$89.47	$89.45	$89.50
Purchase #7	$115.64	12.789%	$130.4292	$130.43	$130.45	$130.40
7 purchase totals =	$662.64		$737.2646	$737.25	$737.25	$737.30