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	$128.95	4.790%	$135.1267	$135.13	$135.15	$135.10
Purchase #2	$48.68	5.627%	$51.4192	$51.42	$51.40	$51.40
Purchase #3	$27.97	13.798%	$31.8293	$31.83	$31.85	$31.80
Purchase #4	$115.40	7.109%	$123.6038	$123.60	$123.60	$123.60
Purchase #5	$25.44	6.468%	$27.0855	$27.09	$27.10	$27.10
Purchase #6	$107.34	4.157%	$111.8021	$111.80	$111.80	$111.80
Purchase #7	$165.78	6.229%	$176.1064	$176.11	$176.10	$176.10
7 purchase totals =	$619.56		$656.9730	$656.98	$657.00	$656.90