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	$148.42	8.127%	$160.4821	$160.48	$160.50	$160.50
Purchase #2	$131.71	4.648%	$137.8319	$137.83	$137.85	$137.80
Purchase #3	$163.55	6.844%	$174.7434	$174.74	$174.75	$174.70
Purchase #4	$224.60	13.768%	$255.5229	$255.52	$255.50	$255.50
Purchase #5	$116.69	3.766%	$121.0845	$121.08	$121.10	$121.10
Purchase #6	$192.46	9.140%	$210.0508	$210.05	$210.05	$210.10
Purchase #7	$119.77	6.158%	$127.1454	$127.15	$127.15	$127.10
7 purchase totals =	$1,097.20		$1,186.8610	$1,186.85	$1,186.90	$1,186.80