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	$20.75	12.870%	$23.4205	$23.42	$23.40	$23.40
Purchase #2	$91.91	8.200%	$99.4466	$99.45	$99.45	$99.40
Purchase #3	$99.93	3.475%	$103.4026	$103.40	$103.40	$103.40
Purchase #4	$23.96	10.531%	$26.4832	$26.48	$26.50	$26.50
Purchase #5	$32.60	8.293%	$35.3035	$35.30	$35.30	$35.30
Purchase #6	$196.72	8.712%	$213.8582	$213.86	$213.85	$213.90
Purchase #7	$173.39	13.386%	$196.6	$196.60	$196.60	$196.60
7 purchase totals =	$639.26		$698.5146	$698.51	$698.50	$698.50