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	$142.98	9.443%	$156.4816	$156.48	$156.50	$156.50
Purchase #2	$53.86	10.357%	$59.4383	$59.44	$59.45	$59.40
Purchase #3	$16.91	4.657%	$17.6975	$17.70	$17.70	$17.70
Purchase #4	$226.44	4.838%	$237.3952	$237.40	$237.40	$237.40
Purchase #5	$239.82	9.609%	$262.8643	$262.86	$262.85	$262.90
Purchase #6	$117.89	4.778%	$123.5228	$123.52	$123.50	$123.50
Purchase #7	$57.26	11.725%	$63.9737	$63.97	$63.95	$64.00
7 purchase totals =	$855.16		$921.3734	$921.37	$921.35	$921.40