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	$136.35	11.753%	$152.3752	$152.38	$152.40	$152.40
Purchase #2	$58.41	6.860%	$62.4169	$62.42	$62.40	$62.40
Purchase #3	$152.57	9.372%	$166.8689	$166.87	$166.85	$166.90
Purchase #4	$89.71	5.832%	$94.9419	$94.94	$94.95	$94.90
Purchase #5	$34.37	8.408%	$37.2598	$37.26	$37.25	$37.30
Purchase #6	$48.50	9.487%	$53.1012	$53.10	$53.10	$53.10
Purchase #7	$65.82	10.470%	$72.7114	$72.71	$72.70	$72.70
7 purchase totals =	$585.73		$639.6753	$639.68	$639.65	$639.70