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	$71.82	12.640%	$80.898	$80.90	$80.90	$80.90
Purchase #2	$247.31	12.866%	$279.1289	$279.13	$279.15	$279.10
Purchase #3	$154.88	8.350%	$167.8125	$167.81	$167.80	$167.80
Purchase #4	$90.81	13.725%	$103.2737	$103.27	$103.25	$103.30
Purchase #5	$222.79	4.683%	$233.2233	$233.22	$233.20	$233.20
Purchase #6	$228.60	12.220%	$256.5349	$256.53	$256.55	$256.50
Purchase #7	$132.55	11.694%	$148.0504	$148.05	$148.05	$148.10
7 purchase totals =	$1,148.76		$1,268.9217	$1,268.91	$1,268.90	$1,268.90