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	$93.70	7.337%	$100.5748	$100.57	$100.55	$100.60
Purchase #2	$125.63	11.123%	$139.6038	$139.60	$139.60	$139.60
Purchase #3	$123.36	6.170%	$130.9713	$130.97	$130.95	$131.00
Purchase #4	$46.58	12.553%	$52.4272	$52.43	$52.45	$52.40
Purchase #5	$230.94	4.636%	$241.6464	$241.65	$241.65	$241.60
Purchase #6	$130.85	12.695%	$147.4614	$147.46	$147.45	$147.50
Purchase #7	$18.77	9.315%	$20.5184	$20.52	$20.50	$20.50
7 purchase totals =	$769.83		$833.2033	$833.20	$833.15	$833.20