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	$200.38	4.311%	$209.0184	$209.02	$209.00	$209.00
Purchase #2	$121.95	12.201%	$136.8291	$136.83	$136.85	$136.80
Purchase #3	$172.28	13.865%	$196.1666	$196.17	$196.15	$196.20
Purchase #4	$211.78	8.728%	$230.2642	$230.26	$230.25	$230.30
Purchase #5	$52.50	8.809%	$57.1247	$57.12	$57.10	$57.10
Purchase #6	$158.48	7.413%	$170.2281	$170.23	$170.25	$170.20
Purchase #7	$224.72	13.854%	$255.8527	$255.85	$255.85	$255.90
7 purchase totals =	$1,142.09		$1,255.4838	$1,255.48	$1,255.45	$1,255.50