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	$89.95	8.374%	$97.4824	$97.48	$97.50	$97.50
Purchase #2	$180.83	10.862%	$200.4718	$200.47	$200.45	$200.50
Purchase #3	$89.75	11.857%	$100.3917	$100.39	$100.40	$100.40
Purchase #4	$206.45	13.365%	$234.042	$234.04	$234.05	$234.00
Purchase #5	$126.50	3.849%	$131.369	$131.37	$131.35	$131.40
Purchase #6	$131.43	4.704%	$137.6125	$137.61	$137.60	$137.60
Purchase #7	$34.81	12.389%	$39.1226	$39.12	$39.10	$39.10
7 purchase totals =	$859.72		$940.4920	$940.48	$940.45	$940.50