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	$84.78	5.666%	$89.5836	$89.58	$89.60	$89.60
Purchase #2	$74.59	12.634%	$84.0137	$84.01	$84.00	$84.00
Purchase #3	$48.86	3.523%	$50.5813	$50.58	$50.60	$50.60
Purchase #4	$23.50	5.601%	$24.8162	$24.82	$24.80	$24.80
Purchase #5	$175.37	9.854%	$192.651	$192.65	$192.65	$192.70
Purchase #6	$68.79	4.434%	$71.8401	$71.84	$71.85	$71.80
Purchase #7	$48.72	11.605%	$54.374	$54.37	$54.35	$54.40
7 purchase totals =	$524.61		$567.8599	$567.85	$567.85	$567.90