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	$241.27	12.405%	$271.1995	$271.20	$271.20	$271.20
Purchase #2	$175.53	12.120%	$196.8042	$196.80	$196.80	$196.80
Purchase #3	$213.47	12.374%	$239.8848	$239.88	$239.90	$239.90
Purchase #4	$20.36	3.201%	$21.0117	$21.01	$21.00	$21.00
Purchase #5	$9.73	10.389%	$10.7408	$10.74	$10.75	$10.70
Purchase #6	$43.51	5.452%	$45.8822	$45.88	$45.90	$45.90
Purchase #7	$45.60	8.241%	$49.3579	$49.36	$49.35	$49.40
7 purchase totals =	$749.47		$834.8811	$834.87	$834.90	$834.90