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	$75.88	3.607%	$78.617	$78.62	$78.60	$78.60
Purchase #2	$34.70	11.520%	$38.6974	$38.70	$38.70	$38.70
Purchase #3	$191.78	13.612%	$217.8851	$217.89	$217.90	$217.90
Purchase #4	$214.64	10.683%	$237.57	$237.57	$237.55	$237.60
Purchase #5	$141.50	3.751%	$146.8077	$146.81	$146.80	$146.80
Purchase #6	$191.95	3.581%	$198.8237	$198.82	$198.80	$198.80
Purchase #7	$63.48	13.302%	$71.9241	$71.92	$71.90	$71.90
7 purchase totals =	$913.93		$990.3250	$990.33	$990.25	$990.30