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	$22.45	6.874%	$23.9932	$23.99	$24.00	$24.00
Purchase #2	$57.55	3.379%	$59.4946	$59.49	$59.50	$59.50
Purchase #3	$20.73	10.786%	$22.9659	$22.97	$22.95	$23.00
Purchase #4	$26.83	9.811%	$29.4623	$29.46	$29.45	$29.50
Purchase #5	$131.29	10.261%	$144.7617	$144.76	$144.75	$144.80
Purchase #6	$47.95	12.484%	$53.9361	$53.94	$53.95	$53.90
Purchase #7	$214.55	3.839%	$222.7866	$222.79	$222.80	$222.80
7 purchase totals =	$521.35		$557.4004	$557.40	$557.40	$557.50