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	$115.65	9.510%	$126.6483	$126.65	$126.65	$126.60
Purchase #2	$212.64	13.139%	$240.5788	$240.58	$240.60	$240.60
Purchase #3	$98.39	13.446%	$111.6195	$111.62	$111.60	$111.60
Purchase #4	$38.60	11.310%	$42.9657	$42.97	$42.95	$43.00
Purchase #5	$250.91	9.770%	$275.4239	$275.42	$275.40	$275.40
Purchase #6	$9.35	4.737%	$9.7929	$9.79	$9.80	$9.80
Purchase #7	$186.50	3.220%	$192.5053	$192.51	$192.50	$192.50
7 purchase totals =	$912.04		$999.5344	$999.54	$999.50	$999.50