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	$49.58	12.109%	$55.5836	$55.58	$55.60	$55.60
Purchase #2	$72.86	13.214%	$82.4877	$82.49	$82.50	$82.50
Purchase #3	$184.52	3.284%	$190.5796	$190.58	$190.60	$190.60
Purchase #4	$65.64	5.680%	$69.3684	$69.37	$69.35	$69.40
Purchase #5	$205.43	11.335%	$228.7155	$228.72	$228.70	$228.70
Purchase #6	$6.94	3.644%	$7.1929	$7.19	$7.20	$7.20
Purchase #7	$245.91	3.819%	$255.3013	$255.30	$255.30	$255.30
7 purchase totals =	$830.88		$889.2290	$889.23	$889.25	$889.30