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	$40.39	8.208%	$43.7052	$43.71	$43.70	$43.70
Purchase #2	$102.72	7.245%	$110.1621	$110.16	$110.15	$110.20
Purchase #3	$90.83	10.400%	$100.2763	$100.28	$100.30	$100.30
Purchase #4	$76.28	10.103%	$83.9866	$83.99	$84.00	$84.00
Purchase #5	$21.48	13.568%	$24.3944	$24.39	$24.40	$24.40
Purchase #6	$119.88	9.243%	$130.9605	$130.96	$130.95	$131.00
Purchase #7	$147.72	13.606%	$167.8188	$167.82	$167.80	$167.80
7 purchase totals =	$599.30		$661.3039	$661.31	$661.30	$661.40