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	$85.51	5.269%	$90.0155	$90.02	$90.00	$90.00
Purchase #2	$12.39	4.255%	$12.9172	$12.92	$12.90	$12.90
Purchase #3	$161.88	3.330%	$167.2706	$167.27	$167.25	$167.30
Purchase #4	$246.58	6.353%	$262.2452	$262.25	$262.25	$262.20
Purchase #5	$48.84	11.726%	$54.567	$54.57	$54.55	$54.60
Purchase #6	$142.58	5.592%	$150.5531	$150.55	$150.55	$150.60
Purchase #7	$89.71	13.395%	$101.7267	$101.73	$101.75	$101.70
7 purchase totals =	$787.49		$839.2953	$839.31	$839.25	$839.30