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	$132.81	8.662%	$144.314	$144.31	$144.30	$144.30
Purchase #2	$241.42	12.227%	$270.9384	$270.94	$270.95	$270.90
Purchase #3	$98.34	7.184%	$105.4047	$105.40	$105.40	$105.40
Purchase #4	$44.89	13.861%	$51.1122	$51.11	$51.10	$51.10
Purchase #5	$105.43	13.647%	$119.818	$119.82	$119.80	$119.80
Purchase #6	$175.84	5.414%	$185.36	$185.36	$185.35	$185.40
Purchase #7	$231.29	5.806%	$244.7187	$244.72	$244.70	$244.70
7 purchase totals =	$1,030.02		$1,121.6660	$1,121.66	$1,121.60	$1,121.60