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	$116.97	4.704%	$122.4723	$122.47	$122.45	$122.50
Purchase #2	$63.39	12.141%	$71.0862	$71.09	$71.10	$71.10
Purchase #3	$114.47	8.225%	$123.8852	$123.89	$123.90	$123.90
Purchase #4	$94.77	5.310%	$99.8023	$99.80	$99.80	$99.80
Purchase #5	$144.28	10.356%	$159.2216	$159.22	$159.20	$159.20
Purchase #6	$27.82	5.873%	$29.4539	$29.45	$29.45	$29.50
Purchase #7	$151.65	9.846%	$166.5815	$166.58	$166.60	$166.60
7 purchase totals =	$713.35		$772.5030	$772.50	$772.50	$772.60