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	$163.91	5.623%	$173.1267	$173.13	$173.15	$173.10
Purchase #2	$169.60	10.749%	$187.8303	$187.83	$187.85	$187.80
Purchase #3	$233.47	11.755%	$260.9144	$260.91	$260.90	$260.90
Purchase #4	$104.95	4.350%	$109.5153	$109.52	$109.50	$109.50
Purchase #5	$43.29	4.288%	$45.1463	$45.15	$45.15	$45.10
Purchase #6	$50.97	6.217%	$54.1388	$54.14	$54.15	$54.10
Purchase #7	$129.67	10.736%	$143.5914	$143.59	$143.60	$143.60
7 purchase totals =	$895.86		$974.2632	$974.27	$974.30	$974.10