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	$102.75	5.683%	$108.5893	$108.59	$108.60	$108.60
Purchase #2	$132.93	3.470%	$137.5427	$137.54	$137.55	$137.50
Purchase #3	$33.69	3.207%	$34.7704	$34.77	$34.75	$34.80
Purchase #4	$149.31	11.256%	$166.1163	$166.12	$166.10	$166.10
Purchase #5	$118.77	7.571%	$127.7621	$127.76	$127.75	$127.80
Purchase #6	$196.88	12.802%	$222.0846	$222.08	$222.10	$222.10
Purchase #7	$34.52	11.508%	$38.4926	$38.49	$38.50	$38.50
7 purchase totals =	$768.85		$835.3580	$835.35	$835.35	$835.40