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	$78.77	3.144%	$81.2465	$81.25	$81.25	$81.20
Purchase #2	$140.88	4.210%	$146.811	$146.81	$146.80	$146.80
Purchase #3	$104.65	6.406%	$111.3539	$111.35	$111.35	$111.40
Purchase #4	$14.29	10.805%	$15.834	$15.83	$15.85	$15.80
Purchase #5	$209.39	11.780%	$234.0561	$234.06	$234.05	$234.10
Purchase #6	$230.78	8.820%	$251.1348	$251.13	$251.15	$251.10
Purchase #7	$169.92	9.365%	$185.833	$185.83	$185.85	$185.80
7 purchase totals =	$948.68		$1,026.2693	$1,026.26	$1,026.30	$1,026.20