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	$100.25	11.213%	$111.491	$111.49	$111.50	$111.50
Purchase #2	$72.33	4.474%	$75.566	$75.57	$75.55	$75.60
Purchase #3	$185.59	11.299%	$206.5598	$206.56	$206.55	$206.60
Purchase #4	$25.79	9.670%	$28.2839	$28.28	$28.30	$28.30
Purchase #5	$60.78	3.639%	$62.9918	$62.99	$63.00	$63.00
Purchase #6	$80.30	12.286%	$90.1657	$90.17	$90.15	$90.20
Purchase #7	$57.49	12.562%	$64.7119	$64.71	$64.70	$64.70
7 purchase totals =	$582.53		$639.7701	$639.77	$639.75	$639.90