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	$81.29	11.543%	$90.6733	$90.67	$90.65	$90.70
Purchase #2	$195.43	5.161%	$205.5161	$205.52	$205.50	$205.50
Purchase #3	$175.31	6.162%	$186.1126	$186.11	$186.10	$186.10
Purchase #4	$175.46	6.723%	$187.2562	$187.26	$187.25	$187.30
Purchase #5	$140.50	13.582%	$159.5827	$159.58	$159.60	$159.60
Purchase #6	$78.40	13.445%	$88.9409	$88.94	$88.95	$88.90
Purchase #7	$212.32	9.776%	$233.0764	$233.08	$233.10	$233.10
7 purchase totals =	$1,058.71		$1,151.1582	$1,151.16	$1,151.15	$1,151.20