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	$229.64	4.603%	$240.2103	$240.21	$240.20	$240.20
Purchase #2	$180.92	12.501%	$203.5368	$203.54	$203.55	$203.50
Purchase #3	$137.30	3.136%	$141.6057	$141.61	$141.60	$141.60
Purchase #4	$12.43	11.453%	$13.8536	$13.85	$13.85	$13.90
Purchase #5	$58.89	12.662%	$66.3467	$66.35	$66.35	$66.30
Purchase #6	$173.57	10.575%	$191.925	$191.93	$191.95	$191.90
Purchase #7	$189.58	5.733%	$200.4486	$200.45	$200.45	$200.40
7 purchase totals =	$982.33		$1,057.9267	$1,057.94	$1,057.95	$1,057.80