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	$80.99	3.574%	$83.8846	$83.88	$83.90	$83.90
Purchase #2	$111.55	4.420%	$116.4805	$116.48	$116.50	$116.50
Purchase #3	$158.65	4.288%	$165.4529	$165.45	$165.45	$165.50
Purchase #4	$203.47	7.871%	$219.4851	$219.49	$219.50	$219.50
Purchase #5	$104.54	5.177%	$109.952	$109.95	$109.95	$110.00
Purchase #6	$85.72	7.486%	$92.137	$92.14	$92.15	$92.10
Purchase #7	$164.72	13.278%	$186.5915	$186.59	$186.60	$186.60
7 purchase totals =	$909.64		$973.9836	$973.98	$974.05	$974.10