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	$142.74	11.782%	$159.5576	$159.56	$159.55	$159.60
Purchase #2	$245.80	6.722%	$262.3227	$262.32	$262.30	$262.30
Purchase #3	$164.50	8.370%	$178.2687	$178.27	$178.25	$178.30
Purchase #4	$145.72	7.398%	$156.5004	$156.50	$156.50	$156.50
Purchase #5	$38.63	9.772%	$42.4049	$42.40	$42.40	$42.40
Purchase #6	$233.72	8.418%	$253.3945	$253.39	$253.40	$253.40
Purchase #7	$198.60	3.692%	$205.9323	$205.93	$205.95	$205.90
7 purchase totals =	$1,169.71		$1,258.3811	$1,258.37	$1,258.35	$1,258.40