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	$103.71	5.393%	$109.3031	$109.30	$109.30	$109.30
Purchase #2	$83.73	9.868%	$91.9925	$91.99	$92.00	$92.00
Purchase #3	$223.85	7.456%	$240.5403	$240.54	$240.55	$240.50
Purchase #4	$56.41	11.177%	$62.7149	$62.71	$62.70	$62.70
Purchase #5	$155.35	11.337%	$172.962	$172.96	$172.95	$173.00
Purchase #6	$74.91	4.532%	$78.3049	$78.30	$78.30	$78.30
Purchase #7	$44.41	7.158%	$47.5889	$47.59	$47.60	$47.60
7 purchase totals =	$742.37		$803.4066	$803.39	$803.40	$803.40