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	$27.29	4.434%	$28.5	$28.50	$28.50	$28.50
Purchase #2	$182.72	4.193%	$190.3814	$190.38	$190.40	$190.40
Purchase #3	$11.72	5.396%	$12.3524	$12.35	$12.35	$12.40
Purchase #4	$192.45	12.322%	$216.1637	$216.16	$216.15	$216.20
Purchase #5	$73.52	12.802%	$82.932	$82.93	$82.95	$82.90
Purchase #6	$166.71	10.190%	$183.6977	$183.70	$183.70	$183.70
Purchase #7	$57.39	8.683%	$62.3732	$62.37	$62.35	$62.40
7 purchase totals =	$711.80		$776.4004	$776.39	$776.40	$776.50