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	$87.73	12.385%	$98.5954	$98.60	$98.60	$98.60
Purchase #2	$117.28	5.385%	$123.5955	$123.60	$123.60	$123.60
Purchase #3	$234.72	8.680%	$255.0937	$255.09	$255.10	$255.10
Purchase #4	$171.42	7.522%	$184.3142	$184.31	$184.30	$184.30
Purchase #5	$17.26	5.346%	$18.1827	$18.18	$18.20	$18.20
Purchase #6	$163.87	8.661%	$178.0628	$178.06	$178.05	$178.10
Purchase #7	$93.84	7.389%	$100.7738	$100.77	$100.75	$100.80
7 purchase totals =	$886.12		$958.6181	$958.61	$958.60	$958.70