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	$131.42	11.728%	$146.8329	$146.83	$146.85	$146.80
Purchase #2	$21.25	11.166%	$23.6228	$23.62	$23.60	$23.60
Purchase #3	$103.77	7.144%	$111.1833	$111.18	$111.20	$111.20
Purchase #4	$205.36	6.474%	$218.655	$218.66	$218.65	$218.70
Purchase #5	$110.93	11.589%	$123.7857	$123.79	$123.80	$123.80
Purchase #6	$68.38	5.781%	$72.333	$72.33	$72.35	$72.30
Purchase #7	$217.26	10.119%	$239.2445	$239.24	$239.25	$239.20
7 purchase totals =	$858.37		$935.6572	$935.65	$935.70	$935.60