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	$35.31	12.251%	$39.6358	$39.64	$39.65	$39.60
Purchase #2	$214.65	8.127%	$232.0946	$232.09	$232.10	$232.10
Purchase #3	$20.90	4.548%	$21.8505	$21.85	$21.85	$21.90
Purchase #4	$203.52	13.295%	$230.578	$230.58	$230.60	$230.60
Purchase #5	$218.94	6.663%	$233.528	$233.53	$233.55	$233.50
Purchase #6	$86.31	3.577%	$89.3973	$89.40	$89.40	$89.40
Purchase #7	$231.56	8.541%	$251.3375	$251.34	$251.35	$251.30
7 purchase totals =	$1,011.19		$1,098.4217	$1,098.43	$1,098.50	$1,098.40