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	$29.98	3.728%	$31.0977	$31.10	$31.10	$31.10
Purchase #2	$166.86	3.574%	$172.8236	$172.82	$172.80	$172.80
Purchase #3	$10.64	12.869%	$12.0093	$12.01	$12.00	$12.00
Purchase #4	$124.75	10.713%	$138.1145	$138.11	$138.10	$138.10
Purchase #5	$234.77	9.214%	$256.4017	$256.40	$256.40	$256.40
Purchase #6	$52.45	5.671%	$55.4244	$55.42	$55.40	$55.40
Purchase #7	$166.55	8.385%	$180.5152	$180.52	$180.50	$180.50
7 purchase totals =	$786.00		$846.3864	$846.38	$846.30	$846.30