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	$100.52	6.266%	$106.8186	$106.82	$106.80	$106.80
Purchase #2	$97.96	13.649%	$111.3306	$111.33	$111.35	$111.30
Purchase #3	$88.93	13.230%	$100.6954	$100.70	$100.70	$100.70
Purchase #4	$220.27	9.445%	$241.0745	$241.07	$241.05	$241.10
Purchase #5	$70.43	7.155%	$75.4693	$75.47	$75.45	$75.50
Purchase #6	$80.72	9.524%	$88.4078	$88.41	$88.40	$88.40
Purchase #7	$34.83	9.156%	$38.019	$38.02	$38.00	$38.00
7 purchase totals =	$693.66		$761.8152	$761.82	$761.75	$761.80