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	$24.77	11.482%	$27.6141	$27.61	$27.60	$27.60
Purchase #2	$233.45	11.866%	$261.1512	$261.15	$261.15	$261.20
Purchase #3	$121.73	7.762%	$131.1787	$131.18	$131.20	$131.20
Purchase #4	$183.76	10.402%	$202.8747	$202.87	$202.85	$202.90
Purchase #5	$38.40	10.520%	$42.4397	$42.44	$42.45	$42.40
Purchase #6	$204.33	5.678%	$215.9319	$215.93	$215.95	$215.90
Purchase #7	$188.49	6.266%	$200.3008	$200.30	$200.30	$200.30
7 purchase totals =	$994.93		$1,081.4911	$1,081.48	$1,081.50	$1,081.50