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	$75.28	5.559%	$79.4648	$79.46	$79.45	$79.50
Purchase #2	$245.83	11.636%	$274.4348	$274.43	$274.45	$274.40
Purchase #3	$110.91	11.438%	$123.5959	$123.60	$123.60	$123.60
Purchase #4	$107.65	8.735%	$117.0532	$117.05	$117.05	$117.10
Purchase #5	$139.64	4.722%	$146.2338	$146.23	$146.25	$146.20
Purchase #6	$83.28	8.413%	$90.2863	$90.29	$90.30	$90.30
Purchase #7	$171.48	3.391%	$177.2949	$177.29	$177.30	$177.30
7 purchase totals =	$934.07		$1,008.3637	$1,008.35	$1,008.40	$1,008.40