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	$20.34	10.241%	$22.423	$22.42	$22.40	$22.40
Purchase #2	$53.65	12.647%	$60.4351	$60.44	$60.45	$60.40
Purchase #3	$215.65	9.397%	$235.9146	$235.91	$235.90	$235.90
Purchase #4	$45.70	12.156%	$51.2553	$51.26	$51.25	$51.30
Purchase #5	$51.54	12.255%	$57.8562	$57.86	$57.85	$57.90
Purchase #6	$43.76	4.737%	$45.8329	$45.83	$45.85	$45.80
Purchase #7	$61.45	8.611%	$66.7415	$66.74	$66.75	$66.70
7 purchase totals =	$492.09		$540.4586	$540.46	$540.45	$540.40