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	$96.43	4.628%	$100.8928	$100.89	$100.90	$100.90
Purchase #2	$214.62	4.593%	$224.4775	$224.48	$224.50	$224.50
Purchase #3	$218.96	5.390%	$230.7619	$230.76	$230.75	$230.80
Purchase #4	$164.86	9.565%	$180.6289	$180.63	$180.65	$180.60
Purchase #5	$33.98	12.338%	$38.1725	$38.17	$38.15	$38.20
Purchase #6	$99.58	12.518%	$112.0454	$112.05	$112.05	$112.00
Purchase #7	$79.72	12.593%	$89.7591	$89.76	$89.75	$89.80
7 purchase totals =	$908.15		$976.7381	$976.74	$976.75	$976.80