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	$59.99	11.338%	$66.7917	$66.79	$66.80	$66.80
Purchase #2	$133.94	4.620%	$140.128	$140.13	$140.15	$140.10
Purchase #3	$99.94	11.558%	$111.4911	$111.49	$111.50	$111.50
Purchase #4	$68.92	9.194%	$75.2565	$75.26	$75.25	$75.30
Purchase #5	$219.86	11.245%	$244.5833	$244.58	$244.60	$244.60
Purchase #6	$89.34	10.776%	$98.9673	$98.97	$98.95	$99.00
Purchase #7	$79.47	7.603%	$85.5121	$85.51	$85.50	$85.50
7 purchase totals =	$751.46		$822.7300	$822.73	$822.75	$822.80