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	$84.81	6.589%	$90.3981	$90.40	$90.40	$90.40
Purchase #2	$43.42	4.731%	$45.4742	$45.47	$45.45	$45.50
Purchase #3	$78.68	7.794%	$84.8123	$84.81	$84.80	$84.80
Purchase #4	$105.86	3.674%	$109.7493	$109.75	$109.75	$109.70
Purchase #5	$89.84	13.221%	$101.7177	$101.72	$101.70	$101.70
Purchase #6	$234.40	3.262%	$242.0461	$242.05	$242.05	$242.00
Purchase #7	$204.69	13.156%	$231.619	$231.62	$231.60	$231.60
7 purchase totals =	$841.70		$905.8167	$905.82	$905.75	$905.70