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	$25.43	7.526%	$27.3439	$27.34	$27.35	$27.30
Purchase #2	$141.64	9.671%	$155.338	$155.34	$155.35	$155.30
Purchase #3	$151.44	13.633%	$172.0858	$172.09	$172.10	$172.10
Purchase #4	$164.95	8.276%	$178.6013	$178.60	$178.60	$178.60
Purchase #5	$20.58	4.298%	$21.4645	$21.46	$21.45	$21.50
Purchase #6	$166.95	3.208%	$172.3058	$172.31	$172.30	$172.30
Purchase #7	$53.79	3.608%	$55.7307	$55.73	$55.75	$55.70
7 purchase totals =	$724.78		$782.8700	$782.87	$782.90	$782.80