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	$17.67	10.860%	$19.589	$19.59	$19.60	$19.60
Purchase #2	$207.91	11.826%	$232.4974	$232.50	$232.50	$232.50
Purchase #3	$64.27	13.109%	$72.6952	$72.70	$72.70	$72.70
Purchase #4	$90.29	3.102%	$93.0908	$93.09	$93.10	$93.10
Purchase #5	$30.54	13.365%	$34.6217	$34.62	$34.60	$34.60
Purchase #6	$141.35	10.457%	$156.131	$156.13	$156.15	$156.10
Purchase #7	$39.30	7.766%	$42.352	$42.35	$42.35	$42.40
7 purchase totals =	$591.33		$650.9771	$650.98	$651.00	$651.00