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	$61.28	4.439%	$64.0002	$64.00	$64.00	$64.00
Purchase #2	$203.45	8.538%	$220.8206	$220.82	$220.80	$220.80
Purchase #3	$197.59	12.462%	$222.2137	$222.21	$222.20	$222.20
Purchase #4	$57.38	9.160%	$62.636	$62.64	$62.65	$62.60
Purchase #5	$153.28	12.227%	$172.0215	$172.02	$172.00	$172.00
Purchase #6	$43.41	4.399%	$45.3196	$45.32	$45.30	$45.30
Purchase #7	$41.50	12.300%	$46.6045	$46.60	$46.60	$46.60
7 purchase totals =	$757.89		$833.6161	$833.61	$833.55	$833.50