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	$223.51	7.738%	$240.8052	$240.81	$240.80	$240.80
Purchase #2	$130.39	10.424%	$143.9819	$143.98	$144.00	$144.00
Purchase #3	$59.71	6.486%	$63.5828	$63.58	$63.60	$63.60
Purchase #4	$152.93	8.792%	$166.3756	$166.38	$166.40	$166.40
Purchase #5	$84.33	6.222%	$89.577	$89.58	$89.60	$89.60
Purchase #6	$130.67	9.833%	$143.5188	$143.52	$143.50	$143.50
Purchase #7	$48.31	4.209%	$50.3434	$50.34	$50.35	$50.30
7 purchase totals =	$829.85		$898.1847	$898.19	$898.25	$898.20