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	$26.93	5.594%	$28.4365	$28.44	$28.45	$28.40
Purchase #2	$132.65	4.477%	$138.5887	$138.59	$138.60	$138.60
Purchase #3	$78.34	6.155%	$83.1618	$83.16	$83.15	$83.20
Purchase #4	$119.75	5.724%	$126.6045	$126.60	$126.60	$126.60
Purchase #5	$112.28	13.535%	$127.4771	$127.48	$127.50	$127.50
Purchase #6	$89.54	13.658%	$101.7694	$101.77	$101.75	$101.80
Purchase #7	$123.86	6.517%	$131.932	$131.93	$131.95	$131.90
7 purchase totals =	$683.35		$737.9700	$737.97	$738.00	$738.00