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	$44.32	13.108%	$50.1295	$50.13	$50.15	$50.10
Purchase #2	$23.30	10.290%	$25.6976	$25.70	$25.70	$25.70
Purchase #3	$65.73	10.392%	$72.5607	$72.56	$72.55	$72.60
Purchase #4	$40.94	4.826%	$42.9158	$42.92	$42.90	$42.90
Purchase #5	$14.31	5.845%	$15.1464	$15.15	$15.15	$15.10
Purchase #6	$62.64	13.368%	$71.0137	$71.01	$71.00	$71.00
Purchase #7	$14.26	8.202%	$15.4296	$15.43	$15.45	$15.40
7 purchase totals =	$265.50		$292.8933	$292.90	$292.90	$292.80