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	$31.25	13.246%	$35.3894	$35.39	$35.40	$35.40
Purchase #2	$38.30	5.603%	$40.4459	$40.45	$40.45	$40.40
Purchase #3	$147.43	13.461%	$167.2756	$167.28	$167.30	$167.30
Purchase #4	$42.67	13.282%	$48.3374	$48.34	$48.35	$48.30
Purchase #5	$43.63	10.659%	$48.2805	$48.28	$48.30	$48.30
Purchase #6	$18.59	10.537%	$20.5488	$20.55	$20.55	$20.50
Purchase #7	$176.59	12.796%	$199.1865	$199.19	$199.20	$199.20
7 purchase totals =	$498.46		$559.4641	$559.48	$559.55	$559.40