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	$57.66	10.815%	$63.8959	$63.90	$63.90	$63.90
Purchase #2	$80.74	11.867%	$90.3214	$90.32	$90.30	$90.30
Purchase #3	$116.86	12.793%	$131.8099	$131.81	$131.80	$131.80
Purchase #4	$215.68	4.477%	$225.336	$225.34	$225.35	$225.30
Purchase #5	$104.25	6.790%	$111.3286	$111.33	$111.35	$111.30
Purchase #6	$33.42	13.189%	$37.8278	$37.83	$37.85	$37.80
Purchase #7	$120.97	9.426%	$132.3726	$132.37	$132.35	$132.40
7 purchase totals =	$729.58		$792.8922	$792.90	$792.90	$792.80