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	$9.52	6.580%	$10.1464	$10.15	$10.15	$10.10
Purchase #2	$40.69	12.590%	$45.8129	$45.81	$45.80	$45.80
Purchase #3	$129.62	13.276%	$146.8284	$146.83	$146.85	$146.80
Purchase #4	$240.28	9.457%	$263.0033	$263.00	$263.00	$263.00
Purchase #5	$136.62	12.600%	$153.8341	$153.83	$153.85	$153.80
Purchase #6	$239.30	8.426%	$259.4634	$259.46	$259.45	$259.50
Purchase #7	$162.67	5.167%	$171.0752	$171.08	$171.10	$171.10
7 purchase totals =	$958.70		$1,050.1637	$1,050.16	$1,050.20	$1,050.10