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	$80.30	8.673%	$87.2644	$87.26	$87.25	$87.30
Purchase #2	$25.50	9.863%	$28.0151	$28.02	$28.00	$28.00
Purchase #3	$79.56	13.712%	$90.4693	$90.47	$90.45	$90.50
Purchase #4	$128.32	11.135%	$142.6084	$142.61	$142.60	$142.60
Purchase #5	$30.75	4.244%	$32.055	$32.06	$32.05	$32.10
Purchase #6	$147.64	10.347%	$162.9163	$162.92	$162.90	$162.90
Purchase #7	$89.35	13.547%	$101.4542	$101.45	$101.45	$101.50
7 purchase totals =	$581.42		$644.7827	$644.79	$644.70	$644.90