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	$82.94	9.601%	$90.9031	$90.90	$90.90	$90.90
Purchase #2	$102.66	12.823%	$115.8241	$115.82	$115.80	$115.80
Purchase #3	$224.42	13.102%	$253.8235	$253.82	$253.80	$253.80
Purchase #4	$37.72	12.539%	$42.4497	$42.45	$42.45	$42.40
Purchase #5	$15.44	13.277%	$17.49	$17.49	$17.50	$17.50
Purchase #6	$117.33	7.551%	$126.1896	$126.19	$126.20	$126.20
Purchase #7	$143.70	5.693%	$151.8808	$151.88	$151.90	$151.90
7 purchase totals =	$724.21		$798.5608	$798.55	$798.55	$798.50