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	$95.72	9.656%	$104.9627	$104.96	$104.95	$105.00
Purchase #2	$55.38	6.314%	$58.8767	$58.88	$58.90	$58.90
Purchase #3	$62.91	11.395%	$70.0786	$70.08	$70.10	$70.10
Purchase #4	$155.90	10.531%	$172.3178	$172.32	$172.30	$172.30
Purchase #5	$18.31	13.376%	$20.7591	$20.76	$20.75	$20.80
Purchase #6	$65.85	12.803%	$74.2808	$74.28	$74.30	$74.30
Purchase #7	$24.59	13.509%	$27.9119	$27.91	$27.90	$27.90
7 purchase totals =	$478.66		$529.1876	$529.19	$529.20	$529.30