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	$32.25	13.150%	$36.4909	$36.49	$36.50	$36.50
Purchase #2	$160.99	7.846%	$173.6213	$173.62	$173.60	$173.60
Purchase #3	$90.48	13.219%	$102.4406	$102.44	$102.45	$102.40
Purchase #4	$76.79	8.871%	$83.602	$83.60	$83.60	$83.60
Purchase #5	$100.73	13.404%	$114.2318	$114.23	$114.25	$114.20
Purchase #6	$31.73	10.570%	$35.0839	$35.08	$35.10	$35.10
Purchase #7	$27.72	13.173%	$31.3716	$31.37	$31.35	$31.40
7 purchase totals =	$520.69		$576.8421	$576.83	$576.85	$576.80