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	$134.41	3.791%	$139.5055	$139.51	$139.50	$139.50
Purchase #2	$231.84	11.287%	$258.0078	$258.01	$258.00	$258.00
Purchase #3	$50.90	3.554%	$52.709	$52.71	$52.70	$52.70
Purchase #4	$29.71	6.434%	$31.6215	$31.62	$31.60	$31.60
Purchase #5	$189.92	4.360%	$198.2005	$198.20	$198.20	$198.20
Purchase #6	$135.89	13.112%	$153.7079	$153.71	$153.70	$153.70
Purchase #7	$173.44	6.429%	$184.5905	$184.59	$184.60	$184.60
7 purchase totals =	$946.11		$1,018.3427	$1,018.35	$1,018.30	$1,018.30