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	$33.45	12.692%	$37.6955	$37.70	$37.70	$37.70
Purchase #2	$33.64	3.359%	$34.77	$34.77	$34.75	$34.80
Purchase #3	$33.62	8.379%	$36.437	$36.44	$36.45	$36.40
Purchase #4	$241.85	7.196%	$259.2535	$259.25	$259.25	$259.30
Purchase #5	$96.91	8.504%	$105.1512	$105.15	$105.15	$105.20
Purchase #6	$114.47	11.172%	$127.2586	$127.26	$127.25	$127.30
Purchase #7	$89.58	7.545%	$96.3388	$96.34	$96.35	$96.30
7 purchase totals =	$643.52		$696.9046	$696.91	$696.90	$697.00