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	$127.86	11.138%	$142.101	$142.10	$142.10	$142.10
Purchase #2	$159.35	4.373%	$166.3184	$166.32	$166.30	$166.30
Purchase #3	$17.96	10.690%	$19.8799	$19.88	$19.90	$19.90
Purchase #4	$176.69	7.177%	$189.371	$189.37	$189.35	$189.40
Purchase #5	$152.96	8.340%	$165.7169	$165.72	$165.70	$165.70
Purchase #6	$135.69	5.737%	$143.4745	$143.47	$143.45	$143.50
Purchase #7	$169.26	12.180%	$189.8759	$189.88	$189.90	$189.90
7 purchase totals =	$939.77		$1,016.7376	$1,016.74	$1,016.70	$1,016.80