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	$38.52	10.155%	$42.4317	$42.43	$42.45	$42.40
Purchase #2	$107.82	8.106%	$116.5599	$116.56	$116.55	$116.60
Purchase #3	$214.70	10.640%	$237.5441	$237.54	$237.55	$237.50
Purchase #4	$124.76	6.163%	$132.449	$132.45	$132.45	$132.40
Purchase #5	$13.90	13.786%	$15.8163	$15.82	$15.80	$15.80
Purchase #6	$159.33	8.252%	$172.4779	$172.48	$172.50	$172.50
Purchase #7	$43.98	3.254%	$45.4111	$45.41	$45.40	$45.40
7 purchase totals =	$703.01		$762.6900	$762.69	$762.70	$762.60