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	$115.30	12.768%	$130.0215	$130.02	$130.00	$130.00
Purchase #2	$72.33	8.348%	$78.3681	$78.37	$78.35	$78.40
Purchase #3	$142.90	7.687%	$153.8847	$153.88	$153.90	$153.90
Purchase #4	$250.27	4.384%	$261.2418	$261.24	$261.25	$261.20
Purchase #5	$124.51	10.660%	$137.7828	$137.78	$137.80	$137.80
Purchase #6	$52.63	7.657%	$56.6599	$56.66	$56.65	$56.70
Purchase #7	$83.74	8.495%	$90.8537	$90.85	$90.85	$90.90
7 purchase totals =	$841.68		$908.8125	$908.80	$908.80	$908.90