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	$81.87	9.309%	$89.4913	$89.49	$89.50	$89.50
Purchase #2	$34.78	7.246%	$37.3002	$37.30	$37.30	$37.30
Purchase #3	$206.69	12.512%	$232.5511	$232.55	$232.55	$232.60
Purchase #4	$23.40	3.230%	$24.1558	$24.16	$24.15	$24.20
Purchase #5	$108.58	13.559%	$123.3024	$123.30	$123.30	$123.30
Purchase #6	$146.31	7.671%	$157.5334	$157.53	$157.55	$157.50
Purchase #7	$16.85	9.551%	$18.4593	$18.46	$18.45	$18.50
7 purchase totals =	$618.48		$682.7935	$682.79	$682.80	$682.90