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	$11.67	7.252%	$12.5163	$12.52	$12.50	$12.50
Purchase #2	$90.60	13.267%	$102.6199	$102.62	$102.60	$102.60
Purchase #3	$81.80	10.287%	$90.2148	$90.21	$90.20	$90.20
Purchase #4	$107.31	7.397%	$115.2477	$115.25	$115.25	$115.20
Purchase #5	$143.98	4.413%	$150.3338	$150.33	$150.35	$150.30
Purchase #6	$11.25	8.553%	$12.2122	$12.21	$12.20	$12.20
Purchase #7	$79.89	8.787%	$86.9099	$86.91	$86.90	$86.90
7 purchase totals =	$526.50		$570.0546	$570.05	$570.00	$569.90