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	$238.94	4.864%	$250.562	$250.56	$250.55	$250.60
Purchase #2	$223.34	12.213%	$250.6165	$250.62	$250.60	$250.60
Purchase #3	$207.96	10.706%	$230.2242	$230.22	$230.20	$230.20
Purchase #4	$182.70	9.672%	$200.3707	$200.37	$200.35	$200.40
Purchase #5	$74.63	10.508%	$82.4721	$82.47	$82.45	$82.50
Purchase #6	$35.54	13.613%	$40.3781	$40.38	$40.40	$40.40
Purchase #7	$40.31	7.337%	$43.2675	$43.27	$43.25	$43.30
7 purchase totals =	$1,003.42		$1,097.8911	$1,097.89	$1,097.80	$1,098.00