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	$17.85	4.505%	$18.6541	$18.65	$18.65	$18.70
Purchase #2	$182.54	4.298%	$190.3856	$190.39	$190.40	$190.40
Purchase #3	$96.39	7.533%	$103.6511	$103.65	$103.65	$103.70
Purchase #4	$206.43	11.224%	$229.5997	$229.60	$229.60	$229.60
Purchase #5	$115.58	6.780%	$123.4163	$123.42	$123.40	$123.40
Purchase #6	$100.91	10.264%	$111.2674	$111.27	$111.25	$111.30
Purchase #7	$139.54	13.664%	$158.6067	$158.61	$158.60	$158.60
7 purchase totals =	$859.24		$935.5809	$935.59	$935.55	$935.70