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	$20.51	4.602%	$21.4539	$21.45	$21.45	$21.50
Purchase #2	$96.85	7.465%	$104.0799	$104.08	$104.10	$104.10
Purchase #3	$98.71	6.372%	$104.9998	$105.00	$105.00	$105.00
Purchase #4	$206.58	4.380%	$215.6282	$215.63	$215.65	$215.60
Purchase #5	$54.60	5.239%	$57.4605	$57.46	$57.45	$57.50
Purchase #6	$28.86	12.725%	$32.5324	$32.53	$32.55	$32.50
Purchase #7	$225.25	3.495%	$233.1225	$233.12	$233.10	$233.10
7 purchase totals =	$731.36		$769.2772	$769.27	$769.30	$769.30