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	$50.74	4.522%	$53.0345	$53.03	$53.05	$53.00
Purchase #2	$121.97	5.657%	$128.8698	$128.87	$128.85	$128.90
Purchase #3	$117.60	8.356%	$127.4267	$127.43	$127.45	$127.40
Purchase #4	$61.91	13.635%	$70.3514	$70.35	$70.35	$70.40
Purchase #5	$16.77	9.709%	$18.3982	$18.40	$18.40	$18.40
Purchase #6	$217.79	5.274%	$229.2762	$229.28	$229.30	$229.30
Purchase #7	$49.53	10.796%	$54.8773	$54.88	$54.90	$54.90
7 purchase totals =	$636.31		$682.2341	$682.24	$682.30	$682.30