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	$240.64	8.553%	$261.2219	$261.22	$261.20	$261.20
Purchase #2	$37.35	7.754%	$40.2461	$40.25	$40.25	$40.20
Purchase #3	$60.50	10.333%	$66.7515	$66.75	$66.75	$66.80
Purchase #4	$116.58	5.682%	$123.2041	$123.20	$123.20	$123.20
Purchase #5	$21.73	3.481%	$22.4864	$22.49	$22.50	$22.50
Purchase #6	$96.96	7.169%	$103.9111	$103.91	$103.90	$103.90
Purchase #7	$59.77	9.708%	$65.5725	$65.57	$65.55	$65.60
7 purchase totals =	$633.53		$683.3936	$683.39	$683.35	$683.40