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	$234.69	9.168%	$256.2064	$256.21	$256.20	$256.20
Purchase #2	$230.39	10.436%	$254.4335	$254.43	$254.45	$254.40
Purchase #3	$50.51	13.276%	$57.2157	$57.22	$57.20	$57.20
Purchase #4	$117.38	12.646%	$132.2239	$132.22	$132.20	$132.20
Purchase #5	$138.54	4.825%	$145.2246	$145.22	$145.20	$145.20
Purchase #6	$193.85	7.372%	$208.1406	$208.14	$208.15	$208.10
Purchase #7	$55.50	5.225%	$58.3999	$58.40	$58.40	$58.40
7 purchase totals =	$1,020.86		$1,111.8446	$1,111.84	$1,111.80	$1,111.70