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	$68.32	3.505%	$70.7146	$70.71	$70.70	$70.70
Purchase #2	$112.66	13.361%	$127.7125	$127.71	$127.70	$127.70
Purchase #3	$108.50	12.560%	$122.1276	$122.13	$122.15	$122.10
Purchase #4	$30.71	5.127%	$32.2845	$32.28	$32.30	$32.30
Purchase #5	$223.45	9.364%	$244.3739	$244.37	$244.35	$244.40
Purchase #6	$163.37	13.712%	$185.7713	$185.77	$185.75	$185.80
Purchase #7	$182.37	4.456%	$190.4964	$190.50	$190.50	$190.50
7 purchase totals =	$889.38		$973.4808	$973.47	$973.45	$973.50