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	$249.89	10.805%	$276.8906	$276.89	$276.90	$276.90
Purchase #2	$147.45	3.436%	$152.5164	$152.52	$152.50	$152.50
Purchase #3	$250.32	13.653%	$284.4962	$284.50	$284.50	$284.50
Purchase #4	$107.79	12.706%	$121.4858	$121.49	$121.50	$121.50
Purchase #5	$173.75	4.789%	$182.0709	$182.07	$182.05	$182.10
Purchase #6	$88.98	13.362%	$100.8695	$100.87	$100.85	$100.90
Purchase #7	$154.74	8.665%	$168.1482	$168.15	$168.15	$168.10
7 purchase totals =	$1,172.92		$1,286.4776	$1,286.49	$1,286.45	$1,286.50