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	$137.64	13.114%	$155.6901	$155.69	$155.70	$155.70
Purchase #2	$25.80	6.644%	$27.5142	$27.51	$27.50	$27.50
Purchase #3	$142.84	6.524%	$152.1589	$152.16	$152.15	$152.20
Purchase #4	$102.94	9.242%	$112.4537	$112.45	$112.45	$112.50
Purchase #5	$116.46	7.117%	$124.7485	$124.75	$124.75	$124.70
Purchase #6	$54.96	7.427%	$59.0419	$59.04	$59.05	$59.00
Purchase #7	$72.59	7.242%	$77.847	$77.85	$77.85	$77.80
7 purchase totals =	$653.23		$709.4543	$709.45	$709.45	$709.40