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	$200.77	10.644%	$222.14	$222.14	$222.15	$222.10
Purchase #2	$77.77	6.493%	$82.8196	$82.82	$82.80	$82.80
Purchase #3	$238.34	6.133%	$252.9574	$252.96	$252.95	$253.00
Purchase #4	$160.45	12.672%	$180.7822	$180.78	$180.80	$180.80
Purchase #5	$131.95	4.190%	$137.4787	$137.48	$137.50	$137.50
Purchase #6	$5.63	4.400%	$5.8777	$5.88	$5.90	$5.90
Purchase #7	$61.58	4.165%	$64.1448	$64.14	$64.15	$64.10
7 purchase totals =	$876.49		$946.2004	$946.20	$946.25	$946.20