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	$37.88	3.612%	$39.2482	$39.25	$39.25	$39.20
Purchase #2	$246.72	6.733%	$263.3317	$263.33	$263.35	$263.30
Purchase #3	$35.66	12.667%	$40.1771	$40.18	$40.20	$40.20
Purchase #4	$52.79	7.256%	$56.6204	$56.62	$56.60	$56.60
Purchase #5	$70.61	8.743%	$76.7834	$76.78	$76.80	$76.80
Purchase #6	$137.27	4.231%	$143.0779	$143.08	$143.10	$143.10
Purchase #7	$33.52	10.694%	$37.1046	$37.10	$37.10	$37.10
7 purchase totals =	$614.45		$656.3433	$656.34	$656.40	$656.30