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	$22.75	6.456%	$24.2187	$24.22	$24.20	$24.20
Purchase #2	$68.40	5.692%	$72.2933	$72.29	$72.30	$72.30
Purchase #3	$64.88	11.537%	$72.3652	$72.37	$72.35	$72.40
Purchase #4	$220.30	3.183%	$227.3121	$227.31	$227.30	$227.30
Purchase #5	$123.45	3.312%	$127.5387	$127.54	$127.55	$127.50
Purchase #6	$234.37	6.680%	$250.0259	$250.03	$250.05	$250.00
Purchase #7	$25.51	7.243%	$27.3577	$27.36	$27.35	$27.40
7 purchase totals =	$759.66		$801.1116	$801.12	$801.10	$801.10