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	$59.49	9.784%	$65.3105	$65.31	$65.30	$65.30
Purchase #2	$144.85	10.603%	$160.2084	$160.21	$160.20	$160.20
Purchase #3	$194.50	12.750%	$219.2988	$219.30	$219.30	$219.30
Purchase #4	$35.86	8.472%	$38.8981	$38.90	$38.90	$38.90
Purchase #5	$203.61	6.799%	$217.4534	$217.45	$217.45	$217.50
Purchase #6	$164.58	4.689%	$172.2972	$172.30	$172.30	$172.30
Purchase #7	$60.71	6.551%	$64.6871	$64.69	$64.70	$64.70
7 purchase totals =	$863.60		$938.1535	$938.16	$938.15	$938.20