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	$51.98	5.422%	$54.7984	$54.80	$54.80	$54.80
Purchase #2	$227.73	5.533%	$240.3303	$240.33	$240.35	$240.30
Purchase #3	$212.52	10.321%	$234.4542	$234.45	$234.45	$234.50
Purchase #4	$126.75	13.797%	$144.2377	$144.24	$144.25	$144.20
Purchase #5	$181.45	10.317%	$200.1702	$200.17	$200.15	$200.20
Purchase #6	$100.43	9.778%	$110.25	$110.25	$110.25	$110.30
Purchase #7	$208.61	7.304%	$223.8469	$223.85	$223.85	$223.80
7 purchase totals =	$1,109.47		$1,208.0877	$1,208.09	$1,208.10	$1,208.10