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	$63.38	12.161%	$71.0876	$71.09	$71.10	$71.10
Purchase #2	$23.60	3.305%	$24.38	$24.38	$24.40	$24.40
Purchase #3	$100.62	8.673%	$109.3468	$109.35	$109.35	$109.30
Purchase #4	$37.53	7.429%	$40.3181	$40.32	$40.30	$40.30
Purchase #5	$199.31	7.677%	$214.611	$214.61	$214.60	$214.60
Purchase #6	$114.31	8.448%	$123.9669	$123.97	$123.95	$124.00
Purchase #7	$101.26	7.695%	$109.052	$109.05	$109.05	$109.10
7 purchase totals =	$640.01		$692.7624	$692.77	$692.75	$692.80