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	$38.75	11.686%	$43.2783	$43.28	$43.30	$43.30
Purchase #2	$105.54	5.283%	$111.1157	$111.12	$111.10	$111.10
Purchase #3	$79.28	8.378%	$85.9221	$85.92	$85.90	$85.90
Purchase #4	$178.31	6.514%	$189.9251	$189.93	$189.95	$189.90
Purchase #5	$153.27	8.859%	$166.8482	$166.85	$166.85	$166.80
Purchase #6	$26.96	10.774%	$29.8647	$29.86	$29.85	$29.90
Purchase #7	$130.91	13.632%	$148.7557	$148.76	$148.75	$148.80
7 purchase totals =	$713.02		$775.7098	$775.72	$775.70	$775.70