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	$39.38	3.130%	$40.6126	$40.61	$40.60	$40.60
Purchase #2	$40.76	3.574%	$42.2168	$42.22	$42.20	$42.20
Purchase #3	$98.65	10.564%	$109.0714	$109.07	$109.05	$109.10
Purchase #4	$72.60	3.595%	$75.21	$75.21	$75.20	$75.20
Purchase #5	$43.54	4.442%	$45.474	$45.47	$45.45	$45.50
Purchase #6	$159.35	8.829%	$173.419	$173.42	$173.40	$173.40
Purchase #7	$20.57	6.663%	$21.9406	$21.94	$21.95	$21.90
7 purchase totals =	$474.85		$507.9444	$507.94	$507.85	$507.90