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	$52.59	8.173%	$56.8882	$56.89	$56.90	$56.90
Purchase #2	$217.87	10.529%	$240.8095	$240.81	$240.80	$240.80
Purchase #3	$103.83	7.186%	$111.2912	$111.29	$111.30	$111.30
Purchase #4	$95.68	6.472%	$101.8724	$101.87	$101.85	$101.90
Purchase #5	$11.84	12.161%	$13.2799	$13.28	$13.30	$13.30
Purchase #6	$120.30	9.753%	$132.0329	$132.03	$132.05	$132.00
Purchase #7	$90.47	7.107%	$96.8997	$96.90	$96.90	$96.90
7 purchase totals =	$692.58		$753.0738	$753.07	$753.10	$753.10