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	$234.62	13.766%	$266.9178	$266.92	$266.90	$266.90
Purchase #2	$161.53	9.465%	$176.8188	$176.82	$176.80	$176.80
Purchase #3	$239.65	10.769%	$265.4579	$265.46	$265.45	$265.50
Purchase #4	$53.61	10.545%	$59.2632	$59.26	$59.25	$59.30
Purchase #5	$172.31	5.627%	$182.0059	$182.01	$182.00	$182.00
Purchase #6	$90.73	13.557%	$103.0303	$103.03	$103.05	$103.00
Purchase #7	$149.66	4.234%	$155.9966	$156.00	$156.00	$156.00
7 purchase totals =	$1,102.11		$1,209.4905	$1,209.50	$1,209.45	$1,209.50