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	$35.63	3.492%	$36.8742	$36.87	$36.85	$36.90
Purchase #2	$133.39	10.443%	$147.3199	$147.32	$147.30	$147.30
Purchase #3	$207.38	11.667%	$231.575	$231.58	$231.60	$231.60
Purchase #4	$83.93	5.435%	$88.4916	$88.49	$88.50	$88.50
Purchase #5	$127.97	12.278%	$143.6822	$143.68	$143.70	$143.70
Purchase #6	$142.47	9.367%	$155.8152	$155.82	$155.80	$155.80
Purchase #7	$93.42	10.800%	$103.5094	$103.51	$103.50	$103.50
7 purchase totals =	$824.19		$907.2675	$907.27	$907.25	$907.30