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	$132.29	4.603%	$138.3793	$138.38	$138.40	$138.40
Purchase #2	$231.46	10.733%	$256.3026	$256.30	$256.30	$256.30
Purchase #3	$72.61	8.776%	$78.9823	$78.98	$79.00	$79.00
Purchase #4	$37.58	7.231%	$40.2974	$40.30	$40.30	$40.30
Purchase #5	$57.88	8.138%	$62.5903	$62.59	$62.60	$62.60
Purchase #6	$232.91	11.562%	$259.8391	$259.84	$259.85	$259.80
Purchase #7	$241.52	5.235%	$254.1636	$254.16	$254.15	$254.20
7 purchase totals =	$1,006.25		$1,090.5546	$1,090.55	$1,090.60	$1,090.60