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	$170.85	5.393%	$180.0639	$180.06	$180.05	$180.10
Purchase #2	$220.71	8.103%	$238.5941	$238.59	$238.60	$238.60
Purchase #3	$104.77	9.677%	$114.9086	$114.91	$114.90	$114.90
Purchase #4	$82.86	8.859%	$90.2006	$90.20	$90.20	$90.20
Purchase #5	$17.27	9.351%	$18.8849	$18.88	$18.90	$18.90
Purchase #6	$98.72	4.527%	$103.1891	$103.19	$103.20	$103.20
Purchase #7	$170.99	9.529%	$187.2836	$187.28	$187.30	$187.30
7 purchase totals =	$866.17		$933.1248	$933.11	$933.15	$933.20