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	$242.86	13.426%	$275.4664	$275.47	$275.45	$275.50
Purchase #2	$33.38	10.264%	$36.8061	$36.81	$36.80	$36.80
Purchase #3	$115.33	10.358%	$127.2759	$127.28	$127.30	$127.30
Purchase #4	$27.26	5.686%	$28.81	$28.81	$28.80	$28.80
Purchase #5	$142.30	11.393%	$158.5122	$158.51	$158.50	$158.50
Purchase #6	$47.99	10.145%	$52.8586	$52.86	$52.85	$52.90
Purchase #7	$137.60	6.589%	$146.6665	$146.67	$146.65	$146.70
7 purchase totals =	$746.72		$826.3957	$826.41	$826.35	$826.50