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	$227.47	12.451%	$255.7923	$255.79	$255.80	$255.80
Purchase #2	$38.66	12.567%	$43.5184	$43.52	$43.50	$43.50
Purchase #3	$161.97	5.782%	$171.3351	$171.34	$171.35	$171.30
Purchase #4	$153.44	3.450%	$158.7337	$158.73	$158.75	$158.70
Purchase #5	$181.64	9.688%	$199.2373	$199.24	$199.25	$199.20
Purchase #6	$132.98	11.841%	$148.7262	$148.73	$148.75	$148.70
Purchase #7	$92.97	12.417%	$104.5141	$104.51	$104.50	$104.50
7 purchase totals =	$989.13		$1,081.8571	$1,081.86	$1,081.90	$1,081.70