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	$61.62	8.210%	$66.679	$66.68	$66.70	$66.70
Purchase #2	$235.34	11.393%	$262.1523	$262.15	$262.15	$262.20
Purchase #3	$83.34	7.484%	$89.5772	$89.58	$89.60	$89.60
Purchase #4	$153.40	13.317%	$173.8283	$173.83	$173.85	$173.80
Purchase #5	$173.67	4.478%	$181.4469	$181.45	$181.45	$181.40
Purchase #6	$117.59	8.649%	$127.7604	$127.76	$127.75	$127.80
Purchase #7	$168.74	12.193%	$189.3145	$189.31	$189.30	$189.30
7 purchase totals =	$993.70		$1,090.7586	$1,090.76	$1,090.80	$1,090.80