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	$140.31	5.718%	$148.3329	$148.33	$148.35	$148.30
Purchase #2	$146.80	9.389%	$160.5831	$160.58	$160.60	$160.60
Purchase #3	$244.53	11.675%	$273.0789	$273.08	$273.10	$273.10
Purchase #4	$150.49	9.353%	$164.5653	$164.57	$164.55	$164.60
Purchase #5	$159.80	12.667%	$180.0419	$180.04	$180.05	$180.00
Purchase #6	$102.38	11.748%	$114.4076	$114.41	$114.40	$114.40
Purchase #7	$92.54	12.850%	$104.4314	$104.43	$104.45	$104.40
7 purchase totals =	$1,036.85		$1,145.4411	$1,145.44	$1,145.50	$1,145.40