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	$137.61	3.619%	$142.5901	$142.59	$142.60	$142.60
Purchase #2	$20.61	4.702%	$21.5791	$21.58	$21.60	$21.60
Purchase #3	$138.43	6.791%	$147.8308	$147.83	$147.85	$147.80
Purchase #4	$170.52	8.683%	$185.3263	$185.33	$185.35	$185.30
Purchase #5	$39.56	10.716%	$43.7992	$43.80	$43.80	$43.80
Purchase #6	$210.36	9.216%	$229.7468	$229.75	$229.75	$229.70
Purchase #7	$27.69	5.476%	$29.2063	$29.21	$29.20	$29.20
7 purchase totals =	$744.78		$800.0786	$800.09	$800.15	$800.00