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	$136.25	4.601%	$142.5189	$142.52	$142.50	$142.50
Purchase #2	$46.43	5.294%	$48.888	$48.89	$48.90	$48.90
Purchase #3	$174.72	6.129%	$185.4286	$185.43	$185.45	$185.40
Purchase #4	$100.81	9.795%	$110.6843	$110.68	$110.70	$110.70
Purchase #5	$122.79	5.347%	$129.3556	$129.36	$129.35	$129.40
Purchase #6	$76.39	9.406%	$83.5752	$83.58	$83.60	$83.60
Purchase #7	$98.78	11.128%	$109.7722	$109.77	$109.75	$109.80
7 purchase totals =	$756.17		$810.2228	$810.23	$810.25	$810.30