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	$51.78	4.675%	$54.2007	$54.20	$54.20	$54.20
Purchase #2	$116.47	11.271%	$129.5973	$129.60	$129.60	$129.60
Purchase #3	$139.59	3.366%	$144.2886	$144.29	$144.30	$144.30
Purchase #4	$90.76	11.620%	$101.3063	$101.31	$101.30	$101.30
Purchase #5	$223.83	5.513%	$236.1697	$236.17	$236.15	$236.20
Purchase #6	$97.42	3.167%	$100.5053	$100.51	$100.50	$100.50
Purchase #7	$63.83	7.109%	$68.3677	$68.37	$68.35	$68.40
7 purchase totals =	$783.68		$834.4356	$834.45	$834.40	$834.50