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	$16.95	10.744%	$18.7711	$18.77	$18.75	$18.80
Purchase #2	$169.90	12.120%	$190.4919	$190.49	$190.50	$190.50
Purchase #3	$156.60	3.720%	$162.4255	$162.43	$162.45	$162.40
Purchase #4	$108.30	5.132%	$113.858	$113.86	$113.85	$113.90
Purchase #5	$235.89	12.224%	$264.7252	$264.73	$264.75	$264.70
Purchase #6	$57.52	7.557%	$61.8668	$61.87	$61.85	$61.90
Purchase #7	$104.29	13.263%	$118.122	$118.12	$118.10	$118.10
7 purchase totals =	$849.45		$930.2605	$930.27	$930.25	$930.30