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	$93.96	9.423%	$102.8139	$102.81	$102.80	$102.80
Purchase #2	$198.58	11.842%	$222.0958	$222.10	$222.10	$222.10
Purchase #3	$180.87	4.482%	$188.9766	$188.98	$189.00	$189.00
Purchase #4	$27.93	5.761%	$29.539	$29.54	$29.55	$29.50
Purchase #5	$65.52	11.198%	$72.8569	$72.86	$72.85	$72.90
Purchase #6	$115.70	6.376%	$123.077	$123.08	$123.10	$123.10
Purchase #7	$228.27	12.515%	$256.838	$256.84	$256.85	$256.80
7 purchase totals =	$910.83		$996.1972	$996.21	$996.25	$996.20