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	$50.66	5.365%	$53.3779	$53.38	$53.40	$53.40
Purchase #2	$158.47	13.540%	$179.9268	$179.93	$179.95	$179.90
Purchase #3	$148.91	3.321%	$153.8553	$153.86	$153.85	$153.90
Purchase #4	$105.81	7.422%	$113.6632	$113.66	$113.65	$113.70
Purchase #5	$61.64	11.266%	$68.5844	$68.58	$68.60	$68.60
Purchase #6	$224.31	6.480%	$238.8453	$238.85	$238.85	$238.80
Purchase #7	$28.65	9.359%	$31.3314	$31.33	$31.35	$31.30
7 purchase totals =	$778.45		$839.5843	$839.59	$839.65	$839.60