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	$246.34	11.870%	$275.5806	$275.58	$275.60	$275.60
Purchase #2	$40.81	13.453%	$46.3002	$46.30	$46.30	$46.30
Purchase #3	$238.86	9.801%	$262.2707	$262.27	$262.25	$262.30
Purchase #4	$43.58	6.277%	$46.3155	$46.32	$46.30	$46.30
Purchase #5	$35.66	11.365%	$39.7128	$39.71	$39.70	$39.70
Purchase #6	$222.62	5.371%	$234.5769	$234.58	$234.60	$234.60
Purchase #7	$51.54	10.176%	$56.7847	$56.78	$56.80	$56.80
7 purchase totals =	$879.41		$961.5414	$961.54	$961.55	$961.60