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	$11.50	10.632%	$12.7227	$12.72	$12.70	$12.70
Purchase #2	$204.85	6.577%	$218.323	$218.32	$218.30	$218.30
Purchase #3	$168.94	7.494%	$181.6004	$181.60	$181.60	$181.60
Purchase #4	$76.46	3.592%	$79.2064	$79.21	$79.20	$79.20
Purchase #5	$117.42	4.804%	$123.0609	$123.06	$123.05	$123.10
Purchase #6	$100.70	4.104%	$104.8327	$104.83	$104.85	$104.80
Purchase #7	$230.85	4.874%	$242.1016	$242.10	$242.10	$242.10
7 purchase totals =	$910.72		$961.8477	$961.84	$961.80	$961.80