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	$185.55	12.739%	$209.1872	$209.19	$209.20	$209.20
Purchase #2	$29.53	8.153%	$31.9376	$31.94	$31.95	$31.90
Purchase #3	$150.52	13.853%	$171.3715	$171.37	$171.35	$171.40
Purchase #4	$41.96	13.227%	$47.51	$47.51	$47.50	$47.50
Purchase #5	$51.88	10.127%	$57.1339	$57.13	$57.15	$57.10
Purchase #6	$167.73	3.333%	$173.3204	$173.32	$173.30	$173.30
Purchase #7	$115.52	11.493%	$128.7967	$128.80	$128.80	$128.80
7 purchase totals =	$742.69		$819.2573	$819.26	$819.25	$819.20