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	$135.80	9.417%	$148.5883	$148.59	$148.60	$148.60
Purchase #2	$137.59	3.627%	$142.5804	$142.58	$142.60	$142.60
Purchase #3	$114.89	11.444%	$128.038	$128.04	$128.05	$128.00
Purchase #4	$122.57	11.376%	$136.5136	$136.51	$136.50	$136.50
Purchase #5	$18.52	9.636%	$20.3046	$20.30	$20.30	$20.30
Purchase #6	$106.91	9.665%	$117.2429	$117.24	$117.25	$117.20
Purchase #7	$60.37	9.748%	$66.2549	$66.25	$66.25	$66.30
7 purchase totals =	$696.65		$759.5227	$759.51	$759.55	$759.50