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	$121.61	12.296%	$136.5632	$136.56	$136.55	$136.60
Purchase #2	$171.42	5.256%	$180.4298	$180.43	$180.45	$180.40
Purchase #3	$235.72	8.521%	$255.8057	$255.81	$255.80	$255.80
Purchase #4	$235.98	11.508%	$263.1366	$263.14	$263.15	$263.10
Purchase #5	$97.41	8.313%	$105.5077	$105.51	$105.50	$105.50
Purchase #6	$90.52	10.208%	$99.7603	$99.76	$99.75	$99.80
Purchase #7	$39.42	6.419%	$41.9504	$41.95	$41.95	$42.00
7 purchase totals =	$992.08		$1,083.1537	$1,083.16	$1,083.15	$1,083.20