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	$249.46	9.675%	$273.5953	$273.60	$273.60	$273.60
Purchase #2	$154.33	11.561%	$172.1721	$172.17	$172.15	$172.20
Purchase #3	$64.35	4.366%	$67.1595	$67.16	$67.15	$67.20
Purchase #4	$97.68	3.344%	$100.9464	$100.95	$100.95	$100.90
Purchase #5	$5.52	10.336%	$6.0905	$6.09	$6.10	$6.10
Purchase #6	$79.79	6.580%	$85.0402	$85.04	$85.05	$85.00
Purchase #7	$108.27	4.212%	$112.8303	$112.83	$112.85	$112.80
7 purchase totals =	$759.40		$817.8343	$817.84	$817.85	$817.80