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	$224.35	11.351%	$249.816	$249.82	$249.80	$249.80
Purchase #2	$70.27	13.607%	$79.8316	$79.83	$79.85	$79.80
Purchase #3	$216.81	3.826%	$225.1052	$225.11	$225.10	$225.10
Purchase #4	$6.38	7.305%	$6.8461	$6.85	$6.85	$6.80
Purchase #5	$137.68	4.707%	$144.1606	$144.16	$144.15	$144.20
Purchase #6	$126.92	12.351%	$142.5959	$142.60	$142.60	$142.60
Purchase #7	$156.60	5.447%	$165.13	$165.13	$165.15	$165.10
7 purchase totals =	$939.01		$1,013.4854	$1,013.50	$1,013.50	$1,013.40