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	$52.78	5.439%	$55.6507	$55.65	$55.65	$55.70
Purchase #2	$140.58	13.616%	$159.7214	$159.72	$159.70	$159.70
Purchase #3	$227.93	4.816%	$238.9071	$238.91	$238.90	$238.90
Purchase #4	$116.83	9.240%	$127.6251	$127.63	$127.65	$127.60
Purchase #5	$102.43	9.264%	$111.9191	$111.92	$111.90	$111.90
Purchase #6	$144.94	11.368%	$161.4168	$161.42	$161.40	$161.40
Purchase #7	$29.73	7.502%	$31.9603	$31.96	$31.95	$32.00
7 purchase totals =	$815.22		$887.2005	$887.21	$887.15	$887.20