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	$207.29	11.206%	$230.5189	$230.52	$230.50	$230.50
Purchase #2	$30.64	12.796%	$34.5607	$34.56	$34.55	$34.60
Purchase #3	$179.47	4.782%	$188.0523	$188.05	$188.05	$188.10
Purchase #4	$147.57	10.236%	$162.6753	$162.68	$162.70	$162.70
Purchase #5	$59.83	8.796%	$65.0926	$65.09	$65.10	$65.10
Purchase #6	$71.31	10.191%	$78.5772	$78.58	$78.60	$78.60
Purchase #7	$27.83	11.821%	$31.1198	$31.12	$31.10	$31.10
7 purchase totals =	$723.94		$790.5968	$790.60	$790.60	$790.70