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	$115.75	6.497%	$123.2703	$123.27	$123.25	$123.30
Purchase #2	$28.80	9.764%	$31.612	$31.61	$31.60	$31.60
Purchase #3	$65.26	8.702%	$70.9389	$70.94	$70.95	$70.90
Purchase #4	$59.55	4.286%	$62.1023	$62.10	$62.10	$62.10
Purchase #5	$55.78	11.548%	$62.2215	$62.22	$62.20	$62.20
Purchase #6	$119.74	11.665%	$133.7077	$133.71	$133.70	$133.70
Purchase #7	$223.25	11.231%	$248.3232	$248.32	$248.30	$248.30
7 purchase totals =	$668.13		$732.1759	$732.17	$732.10	$732.10