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	$158.93	4.526%	$166.1232	$166.12	$166.10	$166.10
Purchase #2	$59.84	11.755%	$66.8742	$66.87	$66.85	$66.90
Purchase #3	$172.85	10.694%	$191.3346	$191.33	$191.35	$191.30
Purchase #4	$68.47	5.551%	$72.2708	$72.27	$72.25	$72.30
Purchase #5	$172.28	7.754%	$185.6386	$185.64	$185.65	$185.60
Purchase #6	$155.73	5.372%	$164.0958	$164.10	$164.10	$164.10
Purchase #7	$211.27	4.131%	$219.9976	$220.00	$220.00	$220.00
7 purchase totals =	$999.37		$1,066.3348	$1,066.33	$1,066.30	$1,066.30