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	$133.82	4.536%	$139.8901	$139.89	$139.90	$139.90
Purchase #2	$141.78	9.732%	$155.578	$155.58	$155.60	$155.60
Purchase #3	$32.72	11.190%	$36.3814	$36.38	$36.40	$36.40
Purchase #4	$229.63	8.152%	$248.3494	$248.35	$248.35	$248.30
Purchase #5	$137.81	4.133%	$143.5057	$143.51	$143.50	$143.50
Purchase #6	$55.25	6.540%	$58.8634	$58.86	$58.85	$58.90
Purchase #7	$208.37	3.295%	$215.2358	$215.24	$215.25	$215.20
7 purchase totals =	$939.38		$997.8038	$997.81	$997.85	$997.80