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	$243.96	4.369%	$254.6186	$254.62	$254.60	$254.60
Purchase #2	$30.30	13.712%	$34.4547	$34.45	$34.45	$34.50
Purchase #3	$50.69	10.176%	$55.8482	$55.85	$55.85	$55.80
Purchase #4	$55.84	7.275%	$59.9024	$59.90	$59.90	$59.90
Purchase #5	$48.71	5.588%	$51.4319	$51.43	$51.45	$51.40
Purchase #6	$63.99	3.830%	$66.4408	$66.44	$66.45	$66.40
Purchase #7	$211.40	10.278%	$233.1277	$233.13	$233.15	$233.10
7 purchase totals =	$704.89		$755.8243	$755.82	$755.85	$755.70