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	$81.25	11.573%	$90.6531	$90.65	$90.65	$90.70
Purchase #2	$231.93	5.483%	$244.6467	$244.65	$244.65	$244.60
Purchase #3	$178.66	7.803%	$192.6008	$192.60	$192.60	$192.60
Purchase #4	$91.27	3.236%	$94.2235	$94.22	$94.20	$94.20
Purchase #5	$194.67	9.157%	$212.4959	$212.50	$212.50	$212.50
Purchase #6	$183.32	13.669%	$208.378	$208.38	$208.40	$208.40
Purchase #7	$136.59	12.565%	$153.7525	$153.75	$153.75	$153.80
7 purchase totals =	$1,097.69		$1,196.7505	$1,196.75	$1,196.75	$1,196.80