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	$40.29	13.135%	$45.5821	$45.58	$45.60	$45.60
Purchase #2	$193.65	11.307%	$215.546	$215.55	$215.55	$215.50
Purchase #3	$28.87	3.347%	$29.8363	$29.84	$29.85	$29.80
Purchase #4	$5.37	9.863%	$5.8996	$5.90	$5.90	$5.90
Purchase #5	$99.88	6.189%	$106.0616	$106.06	$106.05	$106.10
Purchase #6	$146.89	6.424%	$156.3262	$156.33	$156.35	$156.30
Purchase #7	$41.61	4.461%	$43.4662	$43.47	$43.45	$43.50
7 purchase totals =	$556.56		$602.7180	$602.73	$602.75	$602.70