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	$147.79	4.583%	$154.5632	$154.56	$154.55	$154.60
Purchase #2	$36.83	10.276%	$40.6147	$40.61	$40.60	$40.60
Purchase #3	$124.95	10.286%	$137.8024	$137.80	$137.80	$137.80
Purchase #4	$124.39	12.384%	$139.7945	$139.79	$139.80	$139.80
Purchase #5	$223.32	6.729%	$238.3472	$238.35	$238.35	$238.30
Purchase #6	$118.88	4.693%	$124.459	$124.46	$124.45	$124.50
Purchase #7	$139.42	13.331%	$158.0061	$158.01	$158.00	$158.00
7 purchase totals =	$915.58		$993.5871	$993.58	$993.55	$993.60