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	$143.93	4.400%	$150.2629	$150.26	$150.25	$150.30
Purchase #2	$88.50	10.231%	$97.5544	$97.55	$97.55	$97.60
Purchase #3	$18.67	4.834%	$19.5725	$19.57	$19.55	$19.60
Purchase #4	$38.49	9.184%	$42.0249	$42.02	$42.00	$42.00
Purchase #5	$178.93	4.533%	$187.0409	$187.04	$187.05	$187.00
Purchase #6	$45.58	12.632%	$51.3377	$51.34	$51.35	$51.30
Purchase #7	$38.98	4.139%	$40.5934	$40.59	$40.60	$40.60
7 purchase totals =	$553.08		$588.3867	$588.37	$588.35	$588.40