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	$128.55	8.645%	$139.6631	$139.66	$139.65	$139.70
Purchase #2	$51.34	9.462%	$56.1978	$56.20	$56.20	$56.20
Purchase #3	$116.31	12.497%	$130.8453	$130.85	$130.85	$130.80
Purchase #4	$245.32	13.670%	$278.8552	$278.86	$278.85	$278.90
Purchase #5	$55.64	10.589%	$61.5317	$61.53	$61.55	$61.50
Purchase #6	$145.67	4.619%	$152.3985	$152.40	$152.40	$152.40
Purchase #7	$34.74	7.307%	$37.2785	$37.28	$37.30	$37.30
7 purchase totals =	$777.57		$856.7701	$856.78	$856.80	$856.80