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	$57.90	11.705%	$64.6772	$64.68	$64.70	$64.70
Purchase #2	$143.97	12.572%	$162.0699	$162.07	$162.05	$162.10
Purchase #3	$174.88	4.628%	$182.9734	$182.97	$182.95	$183.00
Purchase #4	$213.37	9.614%	$233.8834	$233.88	$233.90	$233.90
Purchase #5	$12.72	4.235%	$13.2587	$13.26	$13.25	$13.30
Purchase #6	$125.52	13.871%	$142.9309	$142.93	$142.95	$142.90
Purchase #7	$53.51	10.801%	$59.2896	$59.29	$59.30	$59.30
7 purchase totals =	$781.87		$859.0831	$859.08	$859.10	$859.20