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	$23.39	4.676%	$24.4837	$24.48	$24.50	$24.50
Purchase #2	$89.48	12.753%	$100.8914	$100.89	$100.90	$100.90
Purchase #3	$168.77	4.553%	$176.4541	$176.45	$176.45	$176.50
Purchase #4	$148.43	12.254%	$166.6186	$166.62	$166.60	$166.60
Purchase #5	$22.87	7.479%	$24.5804	$24.58	$24.60	$24.60
Purchase #6	$80.85	7.423%	$86.8515	$86.85	$86.85	$86.90
Purchase #7	$106.87	3.177%	$110.2653	$110.27	$110.25	$110.30
7 purchase totals =	$640.66		$690.1450	$690.14	$690.15	$690.30