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	$225.35	6.644%	$240.3223	$240.32	$240.30	$240.30
Purchase #2	$33.77	7.555%	$36.3213	$36.32	$36.30	$36.30
Purchase #3	$10.25	5.687%	$10.8329	$10.83	$10.85	$10.80
Purchase #4	$91.57	10.182%	$100.8937	$100.89	$100.90	$100.90
Purchase #5	$138.25	10.396%	$152.6225	$152.62	$152.60	$152.60
Purchase #6	$51.77	13.190%	$58.5985	$58.60	$58.60	$58.60
Purchase #7	$173.74	3.623%	$180.0346	$180.03	$180.05	$180.00
7 purchase totals =	$724.70		$779.6258	$779.61	$779.60	$779.50