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	$133.26	8.644%	$144.779	$144.78	$144.80	$144.80
Purchase #2	$101.58	10.258%	$112.0001	$112.00	$112.00	$112.00
Purchase #3	$100.59	6.522%	$107.1505	$107.15	$107.15	$107.20
Purchase #4	$154.29	3.382%	$159.5081	$159.51	$159.50	$159.50
Purchase #5	$121.73	6.250%	$129.3381	$129.34	$129.35	$129.30
Purchase #6	$239.44	9.206%	$261.4828	$261.48	$261.50	$261.50
Purchase #7	$80.60	11.105%	$89.5506	$89.55	$89.55	$89.60
7 purchase totals =	$931.49		$1,003.8092	$1,003.81	$1,003.85	$1,003.90