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	$219.32	13.577%	$249.0971	$249.10	$249.10	$249.10
Purchase #2	$81.81	9.451%	$89.5419	$89.54	$89.55	$89.50
Purchase #3	$50.96	3.228%	$52.605	$52.61	$52.60	$52.60
Purchase #4	$14.98	5.654%	$15.827	$15.83	$15.85	$15.80
Purchase #5	$32.93	7.326%	$35.3425	$35.34	$35.35	$35.30
Purchase #6	$145.35	10.416%	$160.4897	$160.49	$160.50	$160.50
Purchase #7	$240.38	9.104%	$262.2642	$262.26	$262.25	$262.30
7 purchase totals =	$785.73		$865.1674	$865.17	$865.20	$865.10