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	$30.79	3.158%	$31.7623	$31.76	$31.75	$31.80
Purchase #2	$70.56	9.664%	$77.3789	$77.38	$77.40	$77.40
Purchase #3	$103.36	12.539%	$116.3203	$116.32	$116.30	$116.30
Purchase #4	$168.47	4.228%	$175.5929	$175.59	$175.60	$175.60
Purchase #5	$178.59	10.238%	$196.874	$196.87	$196.85	$196.90
Purchase #6	$98.92	4.300%	$103.1736	$103.17	$103.15	$103.20
Purchase #7	$230.58	8.425%	$250.0064	$250.01	$250.00	$250.00
7 purchase totals =	$881.27		$951.1084	$951.10	$951.05	$951.20