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	$18.53	4.703%	$19.4015	$19.40	$19.40	$19.40
Purchase #2	$112.97	13.447%	$128.1611	$128.16	$128.15	$128.20
Purchase #3	$95.75	12.230%	$107.4602	$107.46	$107.45	$107.50
Purchase #4	$107.80	3.438%	$111.5062	$111.51	$111.50	$111.50
Purchase #5	$167.34	13.367%	$189.7083	$189.71	$189.70	$189.70
Purchase #6	$38.69	11.844%	$43.2724	$43.27	$43.25	$43.30
Purchase #7	$28.73	13.657%	$32.6537	$32.65	$32.65	$32.70
7 purchase totals =	$569.81		$632.1634	$632.16	$632.10	$632.30