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	$15.87	7.361%	$17.0382	$17.04	$17.05	$17.00
Purchase #2	$75.65	3.552%	$78.3371	$78.34	$78.35	$78.30
Purchase #3	$156.59	3.723%	$162.4198	$162.42	$162.40	$162.40
Purchase #4	$9.40	9.633%	$10.3055	$10.31	$10.30	$10.30
Purchase #5	$56.50	11.209%	$62.8331	$62.83	$62.85	$62.80
Purchase #6	$250.82	3.223%	$258.9039	$258.90	$258.90	$258.90
Purchase #7	$129.30	12.200%	$145.0746	$145.07	$145.05	$145.10
7 purchase totals =	$694.13		$734.9122	$734.91	$734.90	$734.80