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	$14.55	6.411%	$15.4828	$15.48	$15.50	$15.50
Purchase #2	$80.33	11.632%	$89.674	$89.67	$89.65	$89.70
Purchase #3	$139.31	4.269%	$145.2571	$145.26	$145.25	$145.30
Purchase #4	$186.91	7.505%	$200.9376	$200.94	$200.95	$200.90
Purchase #5	$205.92	4.340%	$214.8569	$214.86	$214.85	$214.90
Purchase #6	$153.97	10.138%	$169.5795	$169.58	$169.60	$169.60
Purchase #7	$165.60	12.346%	$186.045	$186.05	$186.05	$186.00
7 purchase totals =	$946.59		$1,021.8329	$1,021.84	$1,021.85	$1,021.90