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	$128.69	7.631%	$138.5103	$138.51	$138.50	$138.50
Purchase #2	$151.58	8.565%	$164.5628	$164.56	$164.55	$164.60
Purchase #3	$235.56	10.208%	$259.606	$259.61	$259.60	$259.60
Purchase #4	$30.93	6.509%	$32.9432	$32.94	$32.95	$32.90
Purchase #5	$31.89	4.337%	$33.2731	$33.27	$33.25	$33.30
Purchase #6	$202.52	4.752%	$212.1438	$212.14	$212.15	$212.10
Purchase #7	$100.79	7.441%	$108.2898	$108.29	$108.30	$108.30
7 purchase totals =	$881.96		$949.3290	$949.32	$949.30	$949.30