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	$45.85	4.658%	$47.9857	$47.99	$48.00	$48.00
Purchase #2	$183.83	8.385%	$199.2441	$199.24	$199.25	$199.20
Purchase #3	$18.60	6.521%	$19.8129	$19.81	$19.80	$19.80
Purchase #4	$242.78	6.428%	$258.3859	$258.39	$258.40	$258.40
Purchase #5	$140.49	9.803%	$154.2622	$154.26	$154.25	$154.30
Purchase #6	$79.78	3.389%	$82.4837	$82.48	$82.50	$82.50
Purchase #7	$163.39	13.400%	$185.2843	$185.28	$185.30	$185.30
7 purchase totals =	$874.72		$947.4588	$947.45	$947.50	$947.50