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	$250.84	3.234%	$258.9522	$258.95	$258.95	$259.00
Purchase #2	$216.29	10.420%	$238.8274	$238.83	$238.85	$238.80
Purchase #3	$127.59	11.518%	$142.2858	$142.29	$142.30	$142.30
Purchase #4	$57.56	12.680%	$64.8586	$64.86	$64.85	$64.90
Purchase #5	$98.83	4.659%	$103.4345	$103.43	$103.45	$103.40
Purchase #6	$65.29	8.255%	$70.6797	$70.68	$70.70	$70.70
Purchase #7	$239.49	11.550%	$267.1511	$267.15	$267.15	$267.20
7 purchase totals =	$1,055.89		$1,146.1893	$1,146.19	$1,146.25	$1,146.30