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	$156.36	10.788%	$173.2281	$173.23	$173.25	$173.20
Purchase #2	$20.55	5.131%	$21.6044	$21.60	$21.60	$21.60
Purchase #3	$148.96	8.734%	$161.9702	$161.97	$161.95	$162.00
Purchase #4	$98.83	11.137%	$109.8367	$109.84	$109.85	$109.80
Purchase #5	$103.72	5.111%	$109.0211	$109.02	$109.00	$109.00
Purchase #6	$116.52	4.186%	$121.3975	$121.40	$121.40	$121.40
Purchase #7	$113.77	12.352%	$127.8229	$127.82	$127.80	$127.80
7 purchase totals =	$758.71		$824.8809	$824.88	$824.85	$824.80