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	$47.30	3.361%	$48.8898	$48.89	$48.90	$48.90
Purchase #2	$236.96	7.838%	$255.5329	$255.53	$255.55	$255.50
Purchase #3	$217.25	10.543%	$240.1547	$240.15	$240.15	$240.20
Purchase #4	$64.59	9.141%	$70.4942	$70.49	$70.50	$70.50
Purchase #5	$100.49	7.375%	$107.9011	$107.90	$107.90	$107.90
Purchase #6	$109.37	8.172%	$118.3077	$118.31	$118.30	$118.30
Purchase #7	$40.54	12.529%	$45.6193	$45.62	$45.60	$45.60
7 purchase totals =	$816.50		$886.8997	$886.89	$886.90	$886.90