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	$112.57	9.736%	$123.5298	$123.53	$123.55	$123.50
Purchase #2	$146.70	10.847%	$162.6125	$162.61	$162.60	$162.60
Purchase #3	$24.96	13.792%	$28.4025	$28.40	$28.40	$28.40
Purchase #4	$33.39	7.421%	$35.8679	$35.87	$35.85	$35.90
Purchase #5	$145.28	12.559%	$163.5257	$163.53	$163.55	$163.50
Purchase #6	$210.52	4.572%	$220.145	$220.15	$220.15	$220.10
Purchase #7	$45.51	11.748%	$50.8565	$50.86	$50.85	$50.90
7 purchase totals =	$718.93		$784.9399	$784.95	$784.95	$784.90