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	$194.83	9.594%	$213.522	$213.52	$213.50	$213.50
Purchase #2	$239.89	3.586%	$248.4925	$248.49	$248.50	$248.50
Purchase #3	$18.98	5.583%	$20.0397	$20.04	$20.05	$20.00
Purchase #4	$138.90	8.729%	$151.0246	$151.02	$151.00	$151.00
Purchase #5	$100.69	10.619%	$111.3823	$111.38	$111.40	$111.40
Purchase #6	$83.62	7.658%	$90.0236	$90.02	$90.00	$90.00
Purchase #7	$188.68	10.466%	$208.4272	$208.43	$208.45	$208.40
7 purchase totals =	$965.59		$1,042.9119	$1,042.90	$1,042.90	$1,042.80