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	$73.81	9.599%	$80.895	$80.90	$80.90	$80.90
Purchase #2	$217.27	4.142%	$226.2693	$226.27	$226.25	$226.30
Purchase #3	$204.27	8.737%	$222.1171	$222.12	$222.10	$222.10
Purchase #4	$135.28	7.810%	$145.8454	$145.85	$145.85	$145.80
Purchase #5	$212.52	7.250%	$227.9277	$227.93	$227.95	$227.90
Purchase #6	$82.43	9.525%	$90.2815	$90.28	$90.30	$90.30
Purchase #7	$13.49	10.233%	$14.8704	$14.87	$14.85	$14.90
7 purchase totals =	$939.07		$1,008.2064	$1,008.22	$1,008.20	$1,008.20