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	$16.88	13.311%	$19.1269	$19.13	$19.15	$19.10
Purchase #2	$44.80	11.382%	$49.8991	$49.90	$49.90	$49.90
Purchase #3	$131.55	9.320%	$143.8105	$143.81	$143.80	$143.80
Purchase #4	$223.81	6.613%	$238.6106	$238.61	$238.60	$238.60
Purchase #5	$108.35	10.497%	$119.7235	$119.72	$119.70	$119.70
Purchase #6	$25.37	12.188%	$28.4621	$28.46	$28.45	$28.50
Purchase #7	$57.27	6.505%	$60.9954	$61.00	$61.00	$61.00
7 purchase totals =	$608.03		$660.6281	$660.63	$660.60	$660.60