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	$24.57	11.248%	$27.3336	$27.33	$27.35	$27.30
Purchase #2	$20.65	13.805%	$23.5007	$23.50	$23.50	$23.50
Purchase #3	$123.33	3.680%	$127.8685	$127.87	$127.85	$127.90
Purchase #4	$117.62	8.255%	$127.3295	$127.33	$127.35	$127.30
Purchase #5	$241.50	5.441%	$254.64	$254.64	$254.65	$254.60
Purchase #6	$121.98	10.532%	$134.8269	$134.83	$134.85	$134.80
Purchase #7	$244.86	9.453%	$268.0066	$268.01	$268.00	$268.00
7 purchase totals =	$894.51		$963.5058	$963.51	$963.55	$963.40