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	$142.54	12.287%	$160.0539	$160.05	$160.05	$160.10
Purchase #2	$93.54	13.141%	$105.8321	$105.83	$105.85	$105.80
Purchase #3	$42.58	10.853%	$47.2012	$47.20	$47.20	$47.20
Purchase #4	$188.79	13.404%	$214.0954	$214.10	$214.10	$214.10
Purchase #5	$138.84	8.656%	$150.858	$150.86	$150.85	$150.90
Purchase #6	$220.80	7.789%	$237.9981	$238.00	$238.00	$238.00
Purchase #7	$174.50	12.522%	$196.3509	$196.35	$196.35	$196.40
7 purchase totals =	$1,001.59		$1,112.3896	$1,112.39	$1,112.40	$1,112.50