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	$50.69	6.797%	$54.1354	$54.14	$54.15	$54.10
Purchase #2	$45.68	13.496%	$51.845	$51.85	$51.85	$51.80
Purchase #3	$12.46	3.415%	$12.8855	$12.89	$12.90	$12.90
Purchase #4	$168.41	9.511%	$184.4275	$184.43	$184.45	$184.40
Purchase #5	$227.28	4.642%	$237.8303	$237.83	$237.85	$237.80
Purchase #6	$241.82	11.865%	$270.5119	$270.51	$270.50	$270.50
Purchase #7	$76.47	4.508%	$79.9173	$79.92	$79.90	$79.90
7 purchase totals =	$822.81		$891.5529	$891.57	$891.60	$891.40