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	$25.73	7.321%	$27.6137	$27.61	$27.60	$27.60
Purchase #2	$114.65	7.279%	$122.9954	$123.00	$123.00	$123.00
Purchase #3	$39.37	11.212%	$43.7842	$43.78	$43.80	$43.80
Purchase #4	$102.83	6.418%	$109.4296	$109.43	$109.45	$109.40
Purchase #5	$239.59	9.425%	$262.1714	$262.17	$262.15	$262.20
Purchase #6	$197.88	5.771%	$209.2997	$209.30	$209.30	$209.30
Purchase #7	$151.73	4.544%	$158.6246	$158.62	$158.60	$158.60
7 purchase totals =	$871.78		$933.9186	$933.91	$933.90	$933.90