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	$139.58	4.526%	$145.8974	$145.90	$145.90	$145.90
Purchase #2	$139.55	3.471%	$144.3938	$144.39	$144.40	$144.40
Purchase #3	$30.47	9.379%	$33.3278	$33.33	$33.35	$33.30
Purchase #4	$176.86	3.775%	$183.5365	$183.54	$183.55	$183.50
Purchase #5	$98.78	3.860%	$102.5929	$102.59	$102.60	$102.60
Purchase #6	$232.84	4.871%	$244.1816	$244.18	$244.20	$244.20
Purchase #7	$52.46	7.223%	$56.2492	$56.25	$56.25	$56.20
7 purchase totals =	$870.54		$910.1792	$910.18	$910.25	$910.10