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	$225.87	13.464%	$256.2811	$256.28	$256.30	$256.30
Purchase #2	$109.42	3.406%	$113.1468	$113.15	$113.15	$113.10
Purchase #3	$39.42	4.281%	$41.1076	$41.11	$41.10	$41.10
Purchase #4	$16.29	13.771%	$18.5333	$18.53	$18.55	$18.50
Purchase #5	$17.83	5.456%	$18.8028	$18.80	$18.80	$18.80
Purchase #6	$96.27	12.700%	$108.4963	$108.50	$108.50	$108.50
Purchase #7	$68.93	5.309%	$72.5895	$72.59	$72.60	$72.60
7 purchase totals =	$574.03		$628.9574	$628.96	$629.00	$628.90