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	$61.28	7.841%	$66.085	$66.09	$66.10	$66.10
Purchase #2	$240.40	10.486%	$265.6083	$265.61	$265.60	$265.60
Purchase #3	$68.81	13.832%	$78.3278	$78.33	$78.35	$78.30
Purchase #4	$59.53	10.602%	$65.8414	$65.84	$65.85	$65.80
Purchase #5	$163.64	4.666%	$171.2754	$171.28	$171.30	$171.30
Purchase #6	$98.65	13.859%	$112.3219	$112.32	$112.30	$112.30
Purchase #7	$95.27	4.444%	$99.5038	$99.50	$99.50	$99.50
7 purchase totals =	$787.58		$858.9636	$858.97	$859.00	$858.90