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	$79.39	3.297%	$82.0075	$82.01	$82.00	$82.00
Purchase #2	$45.26	5.143%	$47.5877	$47.59	$47.60	$47.60
Purchase #3	$237.59	12.113%	$266.3693	$266.37	$266.35	$266.40
Purchase #4	$80.51	10.143%	$88.6761	$88.68	$88.70	$88.70
Purchase #5	$55.56	7.598%	$59.7814	$59.78	$59.80	$59.80
Purchase #6	$84.37	6.325%	$89.7064	$89.71	$89.70	$89.70
Purchase #7	$217.91	13.102%	$246.4606	$246.46	$246.45	$246.50
7 purchase totals =	$800.59		$880.5890	$880.60	$880.60	$880.70