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	$140.35	5.647%	$148.2756	$148.28	$148.30	$148.30
Purchase #2	$100.45	12.120%	$112.6245	$112.62	$112.60	$112.60
Purchase #3	$131.76	10.491%	$145.5829	$145.58	$145.60	$145.60
Purchase #4	$104.68	3.496%	$108.3396	$108.34	$108.35	$108.30
Purchase #5	$30.56	5.584%	$32.2665	$32.27	$32.25	$32.30
Purchase #6	$44.32	13.180%	$50.1614	$50.16	$50.15	$50.20
Purchase #7	$168.66	9.291%	$184.3302	$184.33	$184.35	$184.30
7 purchase totals =	$720.78		$781.5807	$781.58	$781.60	$781.60