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	$246.75	13.293%	$279.5505	$279.55	$279.55	$279.60
Purchase #2	$147.80	12.701%	$166.5721	$166.57	$166.55	$166.60
Purchase #3	$237.86	13.867%	$270.844	$270.84	$270.85	$270.80
Purchase #4	$165.35	5.141%	$173.8506	$173.85	$173.85	$173.90
Purchase #5	$83.35	4.743%	$87.3033	$87.30	$87.30	$87.30
Purchase #6	$74.32	10.649%	$82.2343	$82.23	$82.25	$82.20
Purchase #7	$100.77	3.372%	$104.168	$104.17	$104.15	$104.20
7 purchase totals =	$1,056.20		$1,164.5228	$1,164.51	$1,164.50	$1,164.60