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	$156.60	13.849%	$178.2875	$178.29	$178.30	$178.30
Purchase #2	$42.52	7.552%	$45.7311	$45.73	$45.75	$45.70
Purchase #3	$40.85	10.507%	$45.1421	$45.14	$45.15	$45.10
Purchase #4	$189.78	10.292%	$209.3122	$209.31	$209.30	$209.30
Purchase #5	$103.29	8.768%	$112.3465	$112.35	$112.35	$112.30
Purchase #6	$137.55	7.177%	$147.422	$147.42	$147.40	$147.40
Purchase #7	$104.61	7.615%	$112.5761	$112.58	$112.60	$112.60
7 purchase totals =	$775.20		$850.8175	$850.82	$850.85	$850.70