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	$45.69	3.733%	$47.3956	$47.40	$47.40	$47.40
Purchase #2	$178.96	6.584%	$190.7427	$190.74	$190.75	$190.70
Purchase #3	$162.96	8.584%	$176.9485	$176.95	$176.95	$176.90
Purchase #4	$117.86	8.302%	$127.6447	$127.64	$127.65	$127.60
Purchase #5	$146.66	4.529%	$153.3022	$153.30	$153.30	$153.30
Purchase #6	$97.46	12.677%	$109.815	$109.82	$109.80	$109.80
Purchase #7	$13.93	3.771%	$14.4553	$14.46	$14.45	$14.50
7 purchase totals =	$763.52		$820.3040	$820.31	$820.30	$820.20