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	$239.78	13.122%	$271.2439	$271.24	$271.25	$271.20
Purchase #2	$53.88	8.443%	$58.4291	$58.43	$58.45	$58.40
Purchase #3	$72.65	5.432%	$76.5963	$76.60	$76.60	$76.60
Purchase #4	$65.59	3.556%	$67.9224	$67.92	$67.90	$67.90
Purchase #5	$83.50	8.778%	$90.8296	$90.83	$90.85	$90.80
Purchase #6	$157.88	9.515%	$172.9023	$172.90	$172.90	$172.90
Purchase #7	$126.97	11.235%	$141.2351	$141.24	$141.25	$141.20
7 purchase totals =	$800.25		$879.1587	$879.16	$879.20	$879.00