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	$62.89	8.169%	$68.0275	$68.03	$68.05	$68.00
Purchase #2	$74.27	7.871%	$80.1158	$80.12	$80.10	$80.10
Purchase #3	$127.76	13.711%	$145.2772	$145.28	$145.30	$145.30
Purchase #4	$104.64	11.679%	$116.8609	$116.86	$116.85	$116.90
Purchase #5	$247.79	9.185%	$270.5495	$270.55	$270.55	$270.50
Purchase #6	$75.61	13.598%	$85.8914	$85.89	$85.90	$85.90
Purchase #7	$176.51	13.334%	$200.0458	$200.05	$200.05	$200.00
7 purchase totals =	$869.47		$966.7681	$966.78	$966.80	$966.70