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	$86.60	4.804%	$90.7603	$90.76	$90.75	$90.80
Purchase #2	$61.35	11.319%	$68.2942	$68.29	$68.30	$68.30
Purchase #3	$189.86	4.174%	$197.7848	$197.78	$197.80	$197.80
Purchase #4	$112.87	12.872%	$127.3986	$127.40	$127.40	$127.40
Purchase #5	$231.71	11.307%	$257.9094	$257.91	$257.90	$257.90
Purchase #6	$71.77	8.491%	$77.864	$77.86	$77.85	$77.90
Purchase #7	$26.30	5.833%	$27.8341	$27.83	$27.85	$27.80
7 purchase totals =	$780.46		$847.8454	$847.83	$847.85	$847.90