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	$50.74	12.473%	$57.0688	$57.07	$57.05	$57.10
Purchase #2	$129.65	9.459%	$141.9136	$141.91	$141.90	$141.90
Purchase #3	$31.55	7.620%	$33.9541	$33.95	$33.95	$34.00
Purchase #4	$38.70	4.220%	$40.3331	$40.33	$40.35	$40.30
Purchase #5	$101.61	9.843%	$111.6115	$111.61	$111.60	$111.60
Purchase #6	$36.29	6.255%	$38.5599	$38.56	$38.55	$38.60
Purchase #7	$136.91	12.837%	$154.4851	$154.49	$154.50	$154.50
7 purchase totals =	$525.45		$577.9261	$577.92	$577.90	$578.00