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	$14.37	10.659%	$15.9017	$15.90	$15.90	$15.90
Purchase #2	$78.51	9.742%	$86.1584	$86.16	$86.15	$86.20
Purchase #3	$239.93	6.574%	$255.703	$255.70	$255.70	$255.70
Purchase #4	$121.37	6.220%	$128.9192	$128.92	$128.90	$128.90
Purchase #5	$165.51	5.137%	$174.0122	$174.01	$174.00	$174.00
Purchase #6	$95.61	12.517%	$107.5775	$107.58	$107.60	$107.60
Purchase #7	$114.35	11.352%	$127.331	$127.33	$127.35	$127.30
7 purchase totals =	$829.65		$895.6030	$895.60	$895.60	$895.60