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	$228.48	13.599%	$259.551	$259.55	$259.55	$259.60
Purchase #2	$97.30	8.531%	$105.6007	$105.60	$105.60	$105.60
Purchase #3	$89.71	10.109%	$98.7788	$98.78	$98.80	$98.80
Purchase #4	$209.83	11.615%	$234.2018	$234.20	$234.20	$234.20
Purchase #5	$192.98	13.156%	$218.3684	$218.37	$218.35	$218.40
Purchase #6	$164.79	7.604%	$177.3206	$177.32	$177.30	$177.30
Purchase #7	$69.89	12.438%	$78.5829	$78.58	$78.60	$78.60
7 purchase totals =	$1,052.98		$1,172.4042	$1,172.40	$1,172.40	$1,172.50