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	$117.63	3.790%	$122.0882	$122.09	$122.10	$122.10
Purchase #2	$112.62	13.169%	$127.4509	$127.45	$127.45	$127.50
Purchase #3	$162.99	5.525%	$171.9952	$172.00	$172.00	$172.00
Purchase #4	$97.67	12.205%	$109.5906	$109.59	$109.60	$109.60
Purchase #5	$38.31	11.172%	$42.59	$42.59	$42.60	$42.60
Purchase #6	$245.64	10.731%	$271.9996	$272.00	$272.00	$272.00
Purchase #7	$198.41	13.130%	$224.4612	$224.46	$224.45	$224.50
7 purchase totals =	$973.27		$1,070.1757	$1,070.18	$1,070.20	$1,070.30