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	$221.54	12.804%	$249.906	$249.91	$249.90	$249.90
Purchase #2	$175.38	13.330%	$198.7582	$198.76	$198.75	$198.80
Purchase #3	$108.32	5.643%	$114.4325	$114.43	$114.45	$114.40
Purchase #4	$214.47	12.584%	$241.4589	$241.46	$241.45	$241.50
Purchase #5	$166.61	4.692%	$174.4273	$174.43	$174.45	$174.40
Purchase #6	$120.68	5.443%	$127.2486	$127.25	$127.25	$127.20
Purchase #7	$45.43	10.190%	$50.0593	$50.06	$50.05	$50.10
7 purchase totals =	$1,052.43		$1,156.2908	$1,156.30	$1,156.30	$1,156.30