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	$148.39	5.531%	$156.5975	$156.60	$156.60	$156.60
Purchase #2	$233.43	5.201%	$245.5707	$245.57	$245.55	$245.60
Purchase #3	$136.66	8.407%	$148.149	$148.15	$148.15	$148.10
Purchase #4	$245.52	8.254%	$265.7852	$265.79	$265.80	$265.80
Purchase #5	$40.74	5.239%	$42.8744	$42.87	$42.85	$42.90
Purchase #6	$245.83	8.541%	$266.8263	$266.83	$266.85	$266.80
Purchase #7	$138.31	10.680%	$153.0815	$153.08	$153.10	$153.10
7 purchase totals =	$1,188.88		$1,278.8846	$1,278.89	$1,278.90	$1,278.90