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	$19.43	8.494%	$21.0804	$21.08	$21.10	$21.10
Purchase #2	$226.79	5.208%	$238.6012	$238.60	$238.60	$238.60
Purchase #3	$160.79	13.312%	$182.1944	$182.19	$182.20	$182.20
Purchase #4	$139.29	12.820%	$157.147	$157.15	$157.15	$157.10
Purchase #5	$172.82	3.175%	$178.307	$178.31	$178.30	$178.30
Purchase #6	$161.36	4.482%	$168.5922	$168.59	$168.60	$168.60
Purchase #7	$167.27	3.166%	$172.5658	$172.57	$172.55	$172.60
7 purchase totals =	$1,047.75		$1,118.4880	$1,118.49	$1,118.50	$1,118.50