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	$92.69	8.768%	$100.8171	$100.82	$100.80	$100.80
Purchase #2	$118.60	10.672%	$131.257	$131.26	$131.25	$131.30
Purchase #3	$203.84	10.155%	$224.54	$224.54	$224.55	$224.50
Purchase #4	$160.38	3.868%	$166.5835	$166.58	$166.60	$166.60
Purchase #5	$240.41	3.108%	$247.8819	$247.88	$247.90	$247.90
Purchase #6	$43.85	7.591%	$47.1787	$47.18	$47.20	$47.20
Purchase #7	$40.81	7.773%	$43.9822	$43.98	$44.00	$44.00
7 purchase totals =	$900.58		$962.2404	$962.24	$962.30	$962.30