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	$22.88	12.273%	$25.6881	$25.69	$25.70	$25.70
Purchase #2	$231.33	13.828%	$263.3183	$263.32	$263.30	$263.30
Purchase #3	$114.70	4.252%	$119.577	$119.58	$119.60	$119.60
Purchase #4	$215.99	12.755%	$243.5395	$243.54	$243.55	$243.50
Purchase #5	$183.33	4.497%	$191.5744	$191.57	$191.55	$191.60
Purchase #6	$177.96	7.230%	$190.8265	$190.83	$190.85	$190.80
Purchase #7	$61.76	6.823%	$65.9739	$65.97	$65.95	$66.00
7 purchase totals =	$1,007.95		$1,100.4977	$1,100.50	$1,100.50	$1,100.50