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	$180.40	13.434%	$204.6349	$204.63	$204.65	$204.60
Purchase #2	$38.91	12.641%	$43.8286	$43.83	$43.85	$43.80
Purchase #3	$92.33	7.517%	$99.2704	$99.27	$99.25	$99.30
Purchase #4	$241.56	5.278%	$254.3095	$254.31	$254.30	$254.30
Purchase #5	$126.40	9.858%	$138.8605	$138.86	$138.85	$138.90
Purchase #6	$107.34	11.229%	$119.3932	$119.39	$119.40	$119.40
Purchase #7	$86.86	9.223%	$94.8711	$94.87	$94.85	$94.90
7 purchase totals =	$873.80		$955.1682	$955.16	$955.15	$955.20