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	$38.61	3.116%	$39.8131	$39.81	$39.80	$39.80
Purchase #2	$171.37	4.197%	$178.5624	$178.56	$178.55	$178.60
Purchase #3	$124.37	13.768%	$141.4933	$141.49	$141.50	$141.50
Purchase #4	$148.91	5.622%	$157.2817	$157.28	$157.30	$157.30
Purchase #5	$98.97	6.466%	$105.3694	$105.37	$105.35	$105.40
Purchase #6	$6.48	8.211%	$7.0121	$7.01	$7.00	$7.00
Purchase #7	$78.67	13.474%	$89.27	$89.27	$89.25	$89.30
7 purchase totals =	$667.38		$718.8020	$718.79	$718.75	$718.90