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	$50.30	8.555%	$54.6032	$54.60	$54.60	$54.60
Purchase #2	$19.64	7.760%	$21.1641	$21.16	$21.15	$21.20
Purchase #3	$102.36	12.589%	$115.2461	$115.25	$115.25	$115.20
Purchase #4	$36.58	11.820%	$40.9038	$40.90	$40.90	$40.90
Purchase #5	$117.53	12.722%	$132.4822	$132.48	$132.50	$132.50
Purchase #6	$117.84	13.223%	$133.422	$133.42	$133.40	$133.40
Purchase #7	$48.64	4.760%	$50.9553	$50.96	$50.95	$51.00
7 purchase totals =	$492.89		$548.7767	$548.77	$548.75	$548.80