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	$53.56	6.581%	$57.0848	$57.08	$57.10	$57.10
Purchase #2	$187.71	10.874%	$208.1216	$208.12	$208.10	$208.10
Purchase #3	$109.58	13.509%	$124.3832	$124.38	$124.40	$124.40
Purchase #4	$196.36	10.642%	$217.2566	$217.26	$217.25	$217.30
Purchase #5	$46.71	13.414%	$52.9757	$52.98	$53.00	$53.00
Purchase #6	$108.37	9.389%	$118.5449	$118.54	$118.55	$118.50
Purchase #7	$99.78	9.710%	$109.4686	$109.47	$109.45	$109.50
7 purchase totals =	$802.07		$887.8354	$887.83	$887.85	$887.90