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	$39.72	12.742%	$44.7811	$44.78	$44.80	$44.80
Purchase #2	$117.80	6.460%	$125.4099	$125.41	$125.40	$125.40
Purchase #3	$40.64	7.223%	$43.5754	$43.58	$43.60	$43.60
Purchase #4	$155.53	6.613%	$165.8152	$165.82	$165.80	$165.80
Purchase #5	$240.51	13.223%	$272.3126	$272.31	$272.30	$272.30
Purchase #6	$118.73	10.157%	$130.7894	$130.79	$130.80	$130.80
Purchase #7	$148.30	12.509%	$166.8508	$166.85	$166.85	$166.90
7 purchase totals =	$861.23		$949.5344	$949.54	$949.55	$949.60