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	$28.45	4.553%	$29.7453	$29.75	$29.75	$29.70
Purchase #2	$201.37	10.683%	$222.8824	$222.88	$222.90	$222.90
Purchase #3	$10.39	13.357%	$11.7778	$11.78	$11.80	$11.80
Purchase #4	$103.61	13.159%	$117.244	$117.24	$117.25	$117.20
Purchase #5	$26.55	3.747%	$27.5448	$27.54	$27.55	$27.50
Purchase #6	$136.65	6.775%	$145.908	$145.91	$145.90	$145.90
Purchase #7	$81.60	9.298%	$89.1872	$89.19	$89.20	$89.20
7 purchase totals =	$588.62		$644.2895	$644.29	$644.35	$644.20