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	$168.85	4.610%	$176.634	$176.63	$176.65	$176.60
Purchase #2	$103.77	8.585%	$112.6787	$112.68	$112.70	$112.70
Purchase #3	$120.88	5.524%	$127.5574	$127.56	$127.55	$127.60
Purchase #4	$207.86	6.131%	$220.6039	$220.60	$220.60	$220.60
Purchase #5	$77.94	5.802%	$82.4621	$82.46	$82.45	$82.50
Purchase #6	$191.43	6.731%	$204.3152	$204.32	$204.30	$204.30
Purchase #7	$61.30	9.394%	$67.0585	$67.06	$67.05	$67.10
7 purchase totals =	$932.03		$991.3098	$991.31	$991.30	$991.40