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	$138.92	6.816%	$148.3888	$148.39	$148.40	$148.40
Purchase #2	$96.82	4.161%	$100.8487	$100.85	$100.85	$100.80
Purchase #3	$37.45	5.752%	$39.6041	$39.60	$39.60	$39.60
Purchase #4	$52.81	13.488%	$59.933	$59.93	$59.95	$59.90
Purchase #5	$7.72	4.151%	$8.0405	$8.04	$8.05	$8.00
Purchase #6	$141.72	10.172%	$156.1358	$156.14	$156.15	$156.10
Purchase #7	$144.98	4.536%	$151.5563	$151.56	$151.55	$151.60
7 purchase totals =	$620.42		$664.5072	$664.51	$664.55	$664.40