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	$29.77	9.256%	$32.5255	$32.53	$32.55	$32.50
Purchase #2	$209.66	10.358%	$231.3766	$231.38	$231.40	$231.40
Purchase #3	$197.48	4.526%	$206.4179	$206.42	$206.40	$206.40
Purchase #4	$187.30	11.704%	$209.2216	$209.22	$209.20	$209.20
Purchase #5	$98.98	4.696%	$103.6281	$103.63	$103.65	$103.60
Purchase #6	$243.47	5.110%	$255.9113	$255.91	$255.90	$255.90
Purchase #7	$241.84	8.716%	$262.9188	$262.92	$262.90	$262.90
7 purchase totals =	$1,208.50		$1,301.9998	$1,302.01	$1,302.00	$1,301.90