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	$92.35	10.790%	$102.3146	$102.31	$102.30	$102.30
Purchase #2	$33.52	8.370%	$36.3256	$36.33	$36.35	$36.30
Purchase #3	$166.36	11.724%	$185.864	$185.86	$185.85	$185.90
Purchase #4	$63.99	13.718%	$72.7681	$72.77	$72.75	$72.80
Purchase #5	$14.38	9.721%	$15.7779	$15.78	$15.80	$15.80
Purchase #6	$42.64	10.392%	$47.0711	$47.07	$47.05	$47.10
Purchase #7	$112.37	13.706%	$127.7714	$127.77	$127.75	$127.80
7 purchase totals =	$525.61		$587.8927	$587.89	$587.85	$588.00