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	$250.90	13.516%	$284.8116	$284.81	$284.80	$284.80
Purchase #2	$33.37	8.798%	$36.3059	$36.31	$36.30	$36.30
Purchase #3	$244.27	13.384%	$276.9631	$276.96	$276.95	$277.00
Purchase #4	$164.76	9.505%	$180.4204	$180.42	$180.40	$180.40
Purchase #5	$85.99	5.198%	$90.4598	$90.46	$90.45	$90.50
Purchase #6	$9.55	13.422%	$10.8318	$10.83	$10.85	$10.80
Purchase #7	$166.31	9.337%	$181.8384	$181.84	$181.85	$181.80
7 purchase totals =	$955.15		$1,061.6310	$1,061.63	$1,061.60	$1,061.60