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	$179.54	8.172%	$194.212	$194.21	$194.20	$194.20
Purchase #2	$208.59	4.683%	$218.3583	$218.36	$218.35	$218.40
Purchase #3	$100.77	11.673%	$112.5329	$112.53	$112.55	$112.50
Purchase #4	$12.29	9.578%	$13.4671	$13.47	$13.45	$13.50
Purchase #5	$127.50	13.428%	$144.6207	$144.62	$144.60	$144.60
Purchase #6	$82.72	6.436%	$88.0439	$88.04	$88.05	$88.00
Purchase #7	$36.32	12.410%	$40.8273	$40.83	$40.85	$40.80
7 purchase totals =	$747.73		$812.0622	$812.06	$812.05	$812.00