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	$126.54	10.411%	$139.7141	$139.71	$139.70	$139.70
Purchase #2	$84.39	13.735%	$95.981	$95.98	$96.00	$96.00
Purchase #3	$55.90	6.467%	$59.5151	$59.52	$59.50	$59.50
Purchase #4	$203.97	3.587%	$211.2864	$211.29	$211.30	$211.30
Purchase #5	$102.86	9.450%	$112.5803	$112.58	$112.60	$112.60
Purchase #6	$177.95	9.303%	$194.5047	$194.50	$194.50	$194.50
Purchase #7	$191.58	12.374%	$215.2861	$215.29	$215.30	$215.30
7 purchase totals =	$943.19		$1,028.8677	$1,028.87	$1,028.90	$1,028.90