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	$80.51	3.703%	$83.4913	$83.49	$83.50	$83.50
Purchase #2	$82.62	3.599%	$85.5935	$85.59	$85.60	$85.60
Purchase #3	$113.28	12.318%	$127.2338	$127.23	$127.25	$127.20
Purchase #4	$244.78	3.161%	$252.5175	$252.52	$252.50	$252.50
Purchase #5	$132.31	10.248%	$145.8691	$145.87	$145.85	$145.90
Purchase #6	$159.26	5.139%	$167.4444	$167.44	$167.45	$167.40
Purchase #7	$240.52	3.305%	$248.4692	$248.47	$248.45	$248.50
7 purchase totals =	$1,053.28		$1,110.6188	$1,110.61	$1,110.60	$1,110.60