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	$246.52	7.587%	$265.2235	$265.22	$265.20	$265.20
Purchase #2	$163.25	9.694%	$179.0755	$179.08	$179.10	$179.10
Purchase #3	$94.36	6.306%	$100.3103	$100.31	$100.30	$100.30
Purchase #4	$98.59	13.540%	$111.9391	$111.94	$111.95	$111.90
Purchase #5	$77.67	10.203%	$85.5947	$85.59	$85.60	$85.60
Purchase #6	$95.29	5.447%	$100.4804	$100.48	$100.50	$100.50
Purchase #7	$38.83	11.651%	$43.3541	$43.35	$43.35	$43.40
7 purchase totals =	$814.51		$885.9776	$885.97	$886.00	$886.00