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	$51.90	9.406%	$56.7817	$56.78	$56.80	$56.80
Purchase #2	$220.37	9.784%	$241.931	$241.93	$241.95	$241.90
Purchase #3	$248.51	12.288%	$279.0469	$279.05	$279.05	$279.00
Purchase #4	$186.79	12.547%	$210.2265	$210.23	$210.25	$210.20
Purchase #5	$92.65	12.693%	$104.4101	$104.41	$104.40	$104.40
Purchase #6	$123.31	5.871%	$130.5495	$130.55	$130.55	$130.50
Purchase #7	$53.64	11.186%	$59.6402	$59.64	$59.65	$59.60
7 purchase totals =	$977.17		$1,082.5859	$1,082.59	$1,082.65	$1,082.40