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	$56.95	6.250%	$60.5094	$60.51	$60.50	$60.50
Purchase #2	$198.42	12.106%	$222.4407	$222.44	$222.45	$222.40
Purchase #3	$128.95	10.225%	$142.1351	$142.14	$142.15	$142.10
Purchase #4	$47.55	10.596%	$52.5884	$52.59	$52.60	$52.60
Purchase #5	$106.47	7.840%	$114.8172	$114.82	$114.80	$114.80
Purchase #6	$227.95	4.623%	$238.4881	$238.49	$238.50	$238.50
Purchase #7	$136.51	9.406%	$149.3501	$149.35	$149.35	$149.40
7 purchase totals =	$902.80		$980.3290	$980.34	$980.35	$980.30