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	$16.27	12.553%	$18.3124	$18.31	$18.30	$18.30
Purchase #2	$128.93	9.747%	$141.4968	$141.50	$141.50	$141.50
Purchase #3	$64.86	9.353%	$70.9264	$70.93	$70.95	$70.90
Purchase #4	$108.93	13.509%	$123.6454	$123.65	$123.65	$123.60
Purchase #5	$146.62	5.853%	$155.2017	$155.20	$155.20	$155.20
Purchase #6	$220.27	11.478%	$245.5526	$245.55	$245.55	$245.60
Purchase #7	$80.55	7.158%	$86.3158	$86.32	$86.30	$86.30
7 purchase totals =	$766.43		$841.4511	$841.46	$841.45	$841.40