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	$50.81	13.776%	$57.8096	$57.81	$57.80	$57.80
Purchase #2	$49.28	6.133%	$52.3023	$52.30	$52.30	$52.30
Purchase #3	$115.50	10.771%	$127.9405	$127.94	$127.95	$127.90
Purchase #4	$176.89	8.731%	$192.3343	$192.33	$192.35	$192.30
Purchase #5	$132.48	8.577%	$143.8428	$143.84	$143.85	$143.80
Purchase #6	$98.64	5.700%	$104.2625	$104.26	$104.25	$104.30
Purchase #7	$39.79	6.774%	$42.4854	$42.49	$42.50	$42.50
7 purchase totals =	$663.39		$720.9774	$720.97	$721.00	$720.90