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	$86.70	6.342%	$92.1985	$92.20	$92.20	$92.20
Purchase #2	$247.90	9.792%	$272.1744	$272.17	$272.15	$272.20
Purchase #3	$249.81	12.215%	$280.3243	$280.32	$280.30	$280.30
Purchase #4	$142.46	13.845%	$162.1836	$162.18	$162.20	$162.20
Purchase #5	$51.61	10.335%	$56.9439	$56.94	$56.95	$56.90
Purchase #6	$82.29	6.845%	$87.9228	$87.92	$87.90	$87.90
Purchase #7	$174.52	9.207%	$190.5881	$190.59	$190.60	$190.60
7 purchase totals =	$1,035.29		$1,142.3356	$1,142.32	$1,142.30	$1,142.30