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	$36.52	9.653%	$40.0453	$40.05	$40.05	$40.00
Purchase #2	$219.79	8.689%	$238.8876	$238.89	$238.90	$238.90
Purchase #3	$21.79	11.275%	$24.2468	$24.25	$24.25	$24.20
Purchase #4	$43.83	9.646%	$48.0578	$48.06	$48.05	$48.10
Purchase #5	$45.33	13.526%	$51.4613	$51.46	$51.45	$51.50
Purchase #6	$206.25	3.658%	$213.7946	$213.79	$213.80	$213.80
Purchase #7	$38.45	13.381%	$43.595	$43.60	$43.60	$43.60
7 purchase totals =	$611.96		$660.0884	$660.10	$660.10	$660.10