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	$73.60	5.329%	$77.5221	$77.52	$77.50	$77.50
Purchase #2	$148.27	10.644%	$164.0519	$164.05	$164.05	$164.10
Purchase #3	$40.47	7.588%	$43.5409	$43.54	$43.55	$43.50
Purchase #4	$29.39	10.801%	$32.5644	$32.56	$32.55	$32.60
Purchase #5	$6.49	5.439%	$6.843	$6.84	$6.85	$6.80
Purchase #6	$140.99	13.587%	$160.1463	$160.15	$160.15	$160.10
Purchase #7	$185.52	7.838%	$200.0611	$200.06	$200.05	$200.10
7 purchase totals =	$624.73		$684.7297	$684.72	$684.70	$684.70