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	$17.33	7.416%	$18.6152	$18.62	$18.60	$18.60
Purchase #2	$220.88	3.390%	$228.3678	$228.37	$228.35	$228.40
Purchase #3	$225.86	3.640%	$234.0813	$234.08	$234.10	$234.10
Purchase #4	$186.96	3.516%	$193.5335	$193.53	$193.55	$193.50
Purchase #5	$16.31	13.577%	$18.5244	$18.52	$18.50	$18.50
Purchase #6	$80.29	11.472%	$89.5009	$89.50	$89.50	$89.50
Purchase #7	$134.26	6.859%	$143.4689	$143.47	$143.45	$143.50
7 purchase totals =	$881.89		$926.0920	$926.09	$926.05	$926.10