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	$152.78	11.831%	$170.8554	$170.86	$170.85	$170.90
Purchase #2	$140.43	5.609%	$148.3067	$148.31	$148.30	$148.30
Purchase #3	$79.58	13.746%	$90.5191	$90.52	$90.50	$90.50
Purchase #4	$64.88	4.190%	$67.5985	$67.60	$67.60	$67.60
Purchase #5	$228.65	13.535%	$259.5978	$259.60	$259.60	$259.60
Purchase #6	$103.65	4.680%	$108.5008	$108.50	$108.50	$108.50
Purchase #7	$52.61	9.276%	$57.4901	$57.49	$57.50	$57.50
7 purchase totals =	$822.58		$902.8684	$902.88	$902.85	$902.90