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	$215.68	11.182%	$239.7973	$239.80	$239.80	$239.80
Purchase #2	$96.76	3.624%	$100.2666	$100.27	$100.25	$100.30
Purchase #3	$55.79	8.485%	$60.5238	$60.52	$60.50	$60.50
Purchase #4	$47.25	8.503%	$51.2677	$51.27	$51.25	$51.30
Purchase #5	$247.50	5.276%	$260.5581	$260.56	$260.55	$260.60
Purchase #6	$149.50	12.375%	$168.0006	$168.00	$168.00	$168.00
Purchase #7	$88.34	13.479%	$100.2473	$100.25	$100.25	$100.20
7 purchase totals =	$900.82		$980.6614	$980.67	$980.60	$980.70