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	$112.41	13.268%	$127.3246	$127.32	$127.30	$127.30
Purchase #2	$56.44	13.749%	$64.1999	$64.20	$64.20	$64.20
Purchase #3	$141.55	8.558%	$153.6638	$153.66	$153.65	$153.70
Purchase #4	$93.40	7.633%	$100.5292	$100.53	$100.55	$100.50
Purchase #5	$47.77	6.851%	$51.0427	$51.04	$51.05	$51.00
Purchase #6	$42.98	6.699%	$45.8592	$45.86	$45.85	$45.90
Purchase #7	$78.45	4.220%	$81.7606	$81.76	$81.75	$81.80
7 purchase totals =	$573.00		$624.3800	$624.37	$624.35	$624.40